Is Fortran easier to optimize than C for heavy calculations

Question

From time to time I read that Fortran is or can be faster then C for heavy calculations  Is that really true  I must admit that I hardly know Fortran  but the Fortran code I have seen so far did not show that the language has features that C doesn t have   If it is true  please tell me why  Please don t tell me what languages or libs are good for number crunching  I don t intend to write an app or lib to do that  I m just curious

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I was doing some extensive mathematics with FORTRAN and C for a couple of years  From my own experience I can tell that FORTRAN is sometimes really better than C but not for its speed  one can make C perform as fast as FORTRAN by using appropriate coding style  but rather because of very well optimized libraries like LAPACK  and because of great parallelization  On my opinion  FORTRAN is really awkward to work with  and its advantages are not good enough to cancel that drawback  so now I am using C GSL to do calculations

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Any speed differences between Fortran and C will be more a function of compiler optimizations and the underlying math library used by the particular compiler   There is nothing intrinsic to Fortran that would make it faster than C   Anyway  a good programmer can write Fortran in any language

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This is more than somewhat subjective  because it gets into the quality of compilers and such more than anything else  However  to more directly answer your question  speaking from a language compiler standpoint there is nothing about Fortran over C that is going to make it inherently faster or better than C  If you are doing heavy math operations  it will come down to the quality of the compiler  the skill of the programmer in each language and the intrinsic math support libraries that support those operations to ultimately determine which is going to be faster for a given implementation   EDIT  Other people such as  Nils have raised the good point about the difference in the use of pointers in C and the possibility for aliasing that perhaps makes the most naive implementations slower in C  However  there are ways to deal with that in C99  via compiler optimization flags and or in how the C is actually written  This is well covered in  Nils answer and the subsequent comments that follow on his answer

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There is no such thing as one language being faster than another  so the proper answer is no   What you really have to ask is  is code compiled with Fortran compiler X faster than equivalent code compiled with C compiler Y   The answer to that question of course depends on which two compilers you pick   Another question one could ask would be along the lines of  Given the same amount of effort put into optimizing in their compilers  which compiler would produce faster code   The answer to this would in fact be Fortran  Fortran compilers have certian advantages    Fortran had to compete with Assembly back in the day when some vowed never to use compilers  so it was designed for speed  C was designed to be flexible  Fortran s niche has been number crunching  In this domain code is never fast enough  So there s always been a lot of pressure to keep the language efficient  Most of the research in compiler optimizations is done by people interested in speeding up Fortran number crunching code  so optimizing Fortran code is a much better known problem than optimizing any other compiled language  and new innovations show up in Fortran compilers first  Biggie  C encourages much more pointer use than Fortran  This drasticly increases the potential scope of any data item in a C program  which makes them far harder to optimize  Note that Ada is also way better than C in this realm  and is a much more modern OO Language than the commonly found Fortran77  If you want an OO langauge that can generate faster code than C  this is an option for you  Due again to its number-crunching niche  the customers of Fortran compilers tend to care more about optimization than the customers of C compilers    However  there is nothing stopping someone from putting a ton of effort into their C compiler s optimization  and making it generate better code than their platform s Fortran compiler  In fact  the larger sales generated by C compilers makes this scenario quite feasible

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The languages have similar feature-sets  The performance difference comes from the fact that Fortran says aliasing is not allowed  unless an EQUIVALENCE statement is used  Any code that has aliasing is not valid Fortran  but it is up to the programmer and not the compiler to detect these errors  Thus Fortran compilers ignore possible aliasing of memory pointers and allow them to generate more efficient code  Take a look at this little example in C   void transform  float  output  float const   input  float const   matrix  int  n        int i      for  i 0  i lt  n  i                  float x   input i 2 0           float y   input i 2 1           output i 2 0    matrix 0    x   matrix 1    y          output i 2 1    matrix 2    x   matrix 3    y            This function would run slower than the Fortran counterpart after optimization  Why so  If you write values into the output array  you may change the values of matrix  After all  the pointers could overlap and point to the same chunk of memory  including the int pointer    The C compiler is forced to reload the four matrix values from memory for all computations   In Fortran the compiler can load the matrix values once and store them in registers  It can do so because the Fortran compiler assumes pointers arrays do not overlap in memory   Fortunately  the restrict keyword and strict-aliasing have been introduced to the C99 standard to address this problem  It s well supported in most C   compilers these days as well  The keyword allows you to give the compiler a hint that the programmer promises that a pointer does not alias with any other pointer  The strict-aliasing means that the programmer promises that pointers of different type will never overlap  for example a double  will not overlap with an int   with the specific exception that char  and void  can overlap with anything    If you use them you will get the same speed from C and Fortran  However  the ability to use the restrict keyword only with performance critical functions means that C  and C    programs are much safer and easier to write  For example  consider the invalid Fortran code  CALL TRANSFORM A 1  30   A 2  31   A 3  32   30   which most Fortran compilers will happily compile without any warning but introduces a bug that only shows up on some compilers  on some hardware and with some optimization options

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Quick and simple  Both are equally fast  but Fortran is simpler  Whats really faster in the end depends on the algorithm  but there is considerable no speed difference anyway  This is what I learned in a Fortran workshop at high performance computing center Stuttgard  Germany in 2015  I work both with Fortran and C and share this opinion   Explanation   C was designed to write operating systems  Hence it has more freedom than needed to write high performance code  In general this is no problem  but if one does not programm carefully  one can easily slow the code down   Fortran was designed for scientific programming  For this reason  it supports writing fast code syntax-wise  as this is the main purpose of Fortran  In contrast to the public opinion  Fortran is not an outdated programming language  Its latest standard is 2010 and new compilers are published on a regular basis  as most high performance code is writen in Fortran  Fortran further supports modern features as compiler directives  in C pragmas    Example  We want to give a large struct as an input argument to a function  fortran  subroutine   Within the function the argument is not altered   C supports both  call by reference and call by value  which is a handy feature  In our case  the programmer might by accident use call by value  This slows down things considerably  as the struct needs to be copied in within memory first   Fortran works with call by reference only  which forces the programmer to copy the struct by hand  if he really wants a call by value operation  In our case fortran will be automatically as fast as the C version with call by reference

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There is another item where Fortran is different than C - and potentially faster  Fortran has better optimization rules than C   In Fortran  the evaluation order of an expressions is not defined  which allows the compiler to optimize it - if one wants to force a certain order  one has to use parentheses  In C the order is much stricter  but with  -fast  options  they are more relaxed and         are also ignored  I think Fortran has a way which lies nicely in the middle   Well  IEEE makes the live more difficult as certain evaluation-order changes require that no overflows occur  which either has to be ignored or hampers the evaluation    Another area of smarter rules are complex numbers  Not only that it took until C 99 that C had them  also the rules govern them is better in Fortran  since the Fortran library of gfortran is partially written in C but implements the Fortran semantics  GCC gained the option  which can also be used with  normal  C programs       -fcx-fortran-rules   Complex multiplication and division follow Fortran rules   Range reduction is done as part of complex division  but there is no checking whether the result of a complex multiplication or division is  NaN   I NaN   with an attempt to rescue the situation in that case    The alias rules mentioned above is another bonus and also - at least in principle - the whole-array operations  which if taken properly into account by the optimizer of the compiler  can lead faster code  On the contra side are that certain operation take more time  e g  if one does an assignment to an allocatable array  there are lots of checks necessary  reallocate   Fortran 2003 feature   has the array strides  etc    which make the simple operation more complex behind the scenes - and thus slower  but makes the language more powerful  On the other hand  the array operations with flexible bounds and strides makes it easier to write code - and the compiler is usually better optimizing code than a user   In total  I think both C and Fortran are about equally fast  the choice should be more which language does one like more or whether using the whole-array operations of Fortran  and its better portability are more useful -- or the better interfacing to system and graphical-user-interface libraries in C

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Fortran can handle array  especially multidimensional arrays  very conveniently  Slicing elements of multidimensional array in Fortran can be much easier than that in C C    C   now has libraries can do the job  such as Boost or Eigen  but they are after all external libraries  In Fortran these functions are intrinsic    Whether Fortran is faster or more convenient for developing mostly depends on the job you need to finish  As a scientific computation person for geophysics  I did most of computation in Fortran  I mean modern Fortran    F90

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I compare speed of Fortran  C  and C   with the classic Levine-Callahan-Dongarra benchmark from netlib   The multiple language version  with OpenMP  is http   sites google com site tprincesite levine-callahan-dongarra-vectors The C is uglier  as it began with automatic translation  plus insertion of restrict and pragmas for certain compilers  C   is just C with STL templates where applicable   To my view  the STL is a mixed bag as to whether it improves maintainability   There is only minimal exercise of automatic function in-lining to see to what extent it improves optimization  since the examples are based on traditional Fortran practice where little reliance is place on in-lining   The C C   compiler which has by far the most widespread usage lacks auto-vectorization  on which these benchmarks rely heavily   Re the post which came just before this   there are a couple of examples where parentheses are used in Fortran to dictate the faster or more accurate order of evaluation   Known C compilers don t have options to observe the parentheses without disabling more important optimizations

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Most of the posts already present compelling arguments  so I will just add the proverbial 2 cents to a different aspect   Being fortran faster or slower in terms of processing power in the end can have its importance  but if it takes 5 times more time to develop something in Fortran because    it lacks any good library for tasks different from pure number crunching it lack any decent tool for documentation and unit testing it s a language with very low expressivity  skyrocketing the number of lines of code  it has a very poor handling of strings it has an inane amount of issues among different compilers and architectures driving you crazy  it has a very poor IO strategy  READ WRITE of sequential files  Yes  random access files exist but did you ever see them used   it does not encourage good development practices  modularization  effective lack of a fully standard  fully compliant opensource compiler  both gfortran and g95 do not support everything  very poor interoperability with C  mangling  one underscore  two underscores  no underscore  in general one underscore but two if there s another underscore  and just let not delve into COMMON blocks       Then the issue is irrelevant  If something is slow  most of the time you cannot improve it beyond a given limit  If you want something faster  change the algorithm  In the end  computer time is cheap  Human time is not  Value the choice that reduces human time  If it increases computer time  it s cost effective anyway

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I m a hobbyist programmer and i m  average  at both language  I find it easier to write fast Fortran code than C  or C    code  Both Fortran and C are  historic  languages  by today standard   are heavily used  and have well supported free and commercial compiler    I don t know if it s an historic fact but Fortran feel like it s built to be paralleled distributed vectorized whatever-many-cores-ized  And today it s pretty much the  standard metric  when we re talking about speed    does it scale     For pure cpu crunching i love Fortran  For anything IO related i find it easier to work with C   it s difficult in both case anyway    Now of course  for parallel math intensive code you probably want to use your GPU  Both C and Fortran have a lot of more or less well integrated CUDA OpenCL interface  and now OpenACC    My moderately objective answer is   If you know both language equally well poorly then i think Fortran is faster because i find it easier to write parallel distributed code in Fortran than C   once you understood that you can write  freeform  fortran and not just strict F77 code   Here is a 2nd answer for those willing to downvote me because they don t like the 1st answer   Both language have the features required to write high-performance code  So it s dependent of the algorithm you re implementing  cpu intensive   io intensive   memory intensive    the hardware  single cpu   multi-core   distribute supercomputer   GPGPU   FPGA     your skill and ultimately the compiler itself  Both C and Fortran have awesome compiler   i m seriously amazed by how advanced Fortran compilers are but so are C compilers    PS   i m glad you specifically excluded libs because i have a great deal of bad stuff to say about Fortran GUI libs

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The faster code is not really up to the language  is the compiler so you can see the ms-vb  compiler  that generates bloated  slower and redundant object code that is tied together inside an   exe   but powerBasic generates too way better code  Object code made by a C and C   compilers is generated in some phases  at least 2  but by design most Fortran compilers have at least 5 phases including high-level optimizations so by design Fortran will always have the capability to generate highly optimized code  So at the end is the compiler not the language you should ask for  the best compiler i know is the Intel Fortran Compiler because you can get it on LINUX and Windows and you can use VS as the IDE  if you re looking for a cheap tigh compiler you can always relay on OpenWatcom   More info about this  http   ed-thelen org 1401Project 1401-IBM-Systems-Journal-FORTRAN html

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Yes  in 1980  in 2008  depends  When I started programming professionally the speed dominance of Fortran was just being challenged  I remember reading about it in Dr  Dobbs and telling the older programmers about the article--they laughed   So I have two views about this  theoretical and practical  In theory Fortran today has no intrinsic advantage to C C   or even any language that allows assembly code  In practice Fortran today still enjoys the benefits of legacy of a history and culture built around optimization of numerical code   Up until and including Fortran 77  language design considerations had optimization as a main focus  Due to the state of compiler theory and technology  this often meant restricting features and capability in order to give the compiler the best shot at optimizing the code  A good analogy is to think of Fortran 77 as a professional race car that sacrifices features for speed  These days compilers have gotten better across all languages and features for programmer productivity are more valued  However  there are still places where the people are mainly concerned with speed in scientific computing  these people most likely have inherited code  training and culture from people who themselves were Fortran programmers   When one starts talking about optimization of code there are many issues and the best way to get a feel for this is to lurk where people are whose job it is to have fast numerical code  But keep in mind that such critically sensitive code is usually a small fraction of the overall lines of code and very specialized  A lot of Fortran code is just as  inefficient  as a lot of other code in other languages and optimization should not even be a primary concern of such code   A wonderful place to start in learning about the history and culture of Fortran is wikipedia  The Fortran Wikipedia entry is superb and I very much appreciate those who have taken the time and effort to make it of value for the Fortran community    A shortened version of this answer would have been a comment in the excellent thread started by Nils but I don t have the karma to do that  Actually  I probably wouldn t have written anything at all but for that this thread has actual information content and sharing as opposed to flame wars and language bigotry  which is my main experience with this subject  I was overwhelmed and had to share the love

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It is funny that a lot of answers here from not knowing the languages  This is especially true for C C   programmers who have opened and old FORTRAN 77 code and discuss the weaknesses    I suppose that the speed issue is mostly a question between C C   and Fortran  In a Huge code  it always depends on the programmer  There are some features of the language that Fortran outperforms and some features which C does  So  in 2011  no one can really say which one is faster   About the language itself  Fortran nowadays supports Full OOP features and it is fully backward compatible  I have used the Fortran 2003 thoroughly and I would say it was just delightful to use it  In some aspects  Fortran 2003 is still behind C   but let s look at the usage  Fortran is mostly used for Numerical Computation  and nobody uses fancy C   OOP features because of speed reasons  In high performance computing  C   has almost no place to go have a look at the MPI standard and you ll see that C   has been deprecated     Nowadays  you can simply do mixed language programming with Fortran and C C    There are even interfaces for GTK  in Fortran  There are free compilers  gfortran  g95  and many excellent commercial ones

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I compare speed of Fortran  C  and C   with the classic Levine-Callahan-Dongarra benchmark from netlib   The multiple language version  with OpenMP  is http   sites google com site tprincesite levine-callahan-dongarra-vectors The C is uglier  as it began with automatic translation  plus insertion of restrict and pragmas for certain compilers  C   is just C with STL templates where applicable   To my view  the STL is a mixed bag as to whether it improves maintainability   There is only minimal exercise of automatic function in-lining to see to what extent it improves optimization  since the examples are based on traditional Fortran practice where little reliance is place on in-lining   The C C   compiler which has by far the most widespread usage lacks auto-vectorization  on which these benchmarks rely heavily   Re the post which came just before this   there are a couple of examples where parentheses are used in Fortran to dictate the faster or more accurate order of evaluation   Known C compilers don t have options to observe the parentheses without disabling more important optimizations

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There are several reasons why Fortran could be faster  However the amount they matter is so inconsequential or can be worked around anyways  that it shouldn t matter  The main reason to use Fortran nowadays is maintaining or extending legacy applications   PURE and ELEMENTAL keywords on functions  These are functions that have no side effects  This allows optimizations in certain cases where the compiler knows the same function will be called with the same values  Note  GCC implements  quot pure quot  as an extension to the language  Other compilers may as well  Inter-module analysis can also perform this optimization but it is difficult   standard set of functions that deal with arrays  not individual elements  Stuff like sin    log    sqrt   take arrays instead of scalars  This makes it easier to optimize the routine  Auto-vectorization gives the same benefits in most cases if these functions are inline or builtins  Builtin complex type  In theory this could allow the compiler to reorder or eliminate certain instructions in certain cases  but likely you d see the same benefit with the struct   double re  double im     idiom used in C  It makes for faster development though as operators work on complex types in Fortran

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There is another item where Fortran is different than C - and potentially faster  Fortran has better optimization rules than C   In Fortran  the evaluation order of an expressions is not defined  which allows the compiler to optimize it - if one wants to force a certain order  one has to use parentheses  In C the order is much stricter  but with  -fast  options  they are more relaxed and         are also ignored  I think Fortran has a way which lies nicely in the middle   Well  IEEE makes the live more difficult as certain evaluation-order changes require that no overflows occur  which either has to be ignored or hampers the evaluation    Another area of smarter rules are complex numbers  Not only that it took until C 99 that C had them  also the rules govern them is better in Fortran  since the Fortran library of gfortran is partially written in C but implements the Fortran semantics  GCC gained the option  which can also be used with  normal  C programs       -fcx-fortran-rules   Complex multiplication and division follow Fortran rules   Range reduction is done as part of complex division  but there is no checking whether the result of a complex multiplication or division is  NaN   I NaN   with an attempt to rescue the situation in that case    The alias rules mentioned above is another bonus and also - at least in principle - the whole-array operations  which if taken properly into account by the optimizer of the compiler  can lead faster code  On the contra side are that certain operation take more time  e g  if one does an assignment to an allocatable array  there are lots of checks necessary  reallocate   Fortran 2003 feature   has the array strides  etc    which make the simple operation more complex behind the scenes - and thus slower  but makes the language more powerful  On the other hand  the array operations with flexible bounds and strides makes it easier to write code - and the compiler is usually better optimizing code than a user   In total  I think both C and Fortran are about equally fast  the choice should be more which language does one like more or whether using the whole-array operations of Fortran  and its better portability are more useful -- or the better interfacing to system and graphical-user-interface libraries in C

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Using modern standards and compiler  no   Some of the folks here have suggested that FORTRAN is faster because the compiler doesn t need to worry about aliasing  and hence can make more assumptions during optimisation   However  this has been dealt with in C since the C99  I think  standard with the inclusion of the restrict keyword  Which basically tells the compiler  that within a give scope  the pointer is not aliased  Furthermore C enables proper pointer arithmetic  where things like aliasing can be very useful in terms of performance and resource allocation  Although I think more recent version of FORTRAN enable the use of  proper  pointers   For modern implementations C general outperforms FORTRAN  although it is very fast too    http   benchmarksgame alioth debian org u64q fortran html  EDIT   A fair criticism of this seems to be that the benchmarking may be biased  Here is another source  relative to C  that puts result in more context   http   julialang org benchmarks   You can see that C typically outperforms Fortran in most instances  again see criticisms below that apply here too   as others have stated  benchmarking is an inexact science that can be easily loaded to favour one language over others  But it does put in context how Fortran and C have similar performance

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I think the key point in favor of Fortran is that it is a language slightly more suited for expressing vector- and array-based math   The pointer analysis issue pointed out above is real in practice  since portable code cannot really assume that you can tell a compiler something   There is ALWAYS an advantage to expression computaitons in a manner closer to how the domain looks   C does not really have arrays at all  if  you look closely  just something that kind of behaves like it  Fortran has real arrawys  Which makes it easier to compile for certain types of algorithms especially for parallel machines    Deep down in things like run-time system and calling conventions  C and modern Fortran are sufficiently similar that it is hard to see what would make a difference   Note that C here is really base C  C   is a totally different issue with very different performance characteristics

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Fortran traditionally doesn t set options such as -fp strict  which ifort requires to enable some of the features in USE IEEE arithmetic  a part of f2003 standard    Intel C   also doesn t set -fp strict as a default  but that is required for ERRNO handling  for example  and other C   compilers don t make it convenient to turn off ERRNO or gain optimizations such as simd reduction  gcc and g   have required me to set up Makefile to avoid using the dangerous combination -O3 -ffast-math -fopenmp -march native  Other than these issues  this question about relative performance gets more nit-picky and dependent on local rules about choice of compilers and options

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To some extent Fortran has been designed keeping compiler optimization in mind  The language supports whole array operations where compilers can exploit parallelism  specially on multi-core processors   For example   Dense matrix multiplication is simply   matmul a b    L2 norm of a vector x is   sqrt sum x  2     Moreover statements such as FORALL  PURE  amp  ELEMENTAL procedures etc  further help to optimize code  Even pointers in Fortran arent as flexible as C because of this simple reason   The upcoming Fortran standard  2008  has co-arrays which allows you to easily write parallel code  G95  open source  and compilers from CRAY already support it    So yes Fortran can be fast simply because compilers can optimize parallelize it better than C C    But again like everything else in life there are good compilers and bad compilers

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Yes  in 1980  in 2008  depends  When I started programming professionally the speed dominance of Fortran was just being challenged  I remember reading about it in Dr  Dobbs and telling the older programmers about the article--they laughed   So I have two views about this  theoretical and practical  In theory Fortran today has no intrinsic advantage to C C   or even any language that allows assembly code  In practice Fortran today still enjoys the benefits of legacy of a history and culture built around optimization of numerical code   Up until and including Fortran 77  language design considerations had optimization as a main focus  Due to the state of compiler theory and technology  this often meant restricting features and capability in order to give the compiler the best shot at optimizing the code  A good analogy is to think of Fortran 77 as a professional race car that sacrifices features for speed  These days compilers have gotten better across all languages and features for programmer productivity are more valued  However  there are still places where the people are mainly concerned with speed in scientific computing  these people most likely have inherited code  training and culture from people who themselves were Fortran programmers   When one starts talking about optimization of code there are many issues and the best way to get a feel for this is to lurk where people are whose job it is to have fast numerical code  But keep in mind that such critically sensitive code is usually a small fraction of the overall lines of code and very specialized  A lot of Fortran code is just as  inefficient  as a lot of other code in other languages and optimization should not even be a primary concern of such code   A wonderful place to start in learning about the history and culture of Fortran is wikipedia  The Fortran Wikipedia entry is superb and I very much appreciate those who have taken the time and effort to make it of value for the Fortran community    A shortened version of this answer would have been a comment in the excellent thread started by Nils but I don t have the karma to do that  Actually  I probably wouldn t have written anything at all but for that this thread has actual information content and sharing as opposed to flame wars and language bigotry  which is my main experience with this subject  I was overwhelmed and had to share the love

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Fortran has better I O routines  e g  the implied do facility gives flexibility that C s standard library can t match    The Fortran compiler directly handles the more complex  syntax involved  and as such syntax can t be easily reduced  to argument passing form  C can t implement it efficiently

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There is no such thing as one language being faster than another  so the proper answer is no   What you really have to ask is  is code compiled with Fortran compiler X faster than equivalent code compiled with C compiler Y   The answer to that question of course depends on which two compilers you pick   Another question one could ask would be along the lines of  Given the same amount of effort put into optimizing in their compilers  which compiler would produce faster code   The answer to this would in fact be Fortran  Fortran compilers have certian advantages    Fortran had to compete with Assembly back in the day when some vowed never to use compilers  so it was designed for speed  C was designed to be flexible  Fortran s niche has been number crunching  In this domain code is never fast enough  So there s always been a lot of pressure to keep the language efficient  Most of the research in compiler optimizations is done by people interested in speeding up Fortran number crunching code  so optimizing Fortran code is a much better known problem than optimizing any other compiled language  and new innovations show up in Fortran compilers first  Biggie  C encourages much more pointer use than Fortran  This drasticly increases the potential scope of any data item in a C program  which makes them far harder to optimize  Note that Ada is also way better than C in this realm  and is a much more modern OO Language than the commonly found Fortran77  If you want an OO langauge that can generate faster code than C  this is an option for you  Due again to its number-crunching niche  the customers of Fortran compilers tend to care more about optimization than the customers of C compilers    However  there is nothing stopping someone from putting a ton of effort into their C compiler s optimization  and making it generate better code than their platform s Fortran compiler  In fact  the larger sales generated by C compilers makes this scenario quite feasible

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There is nothing about the languages Fortran and C which makes one faster than the other for specific purposes   There are things about specific compilers for each of these languages which make some favorable for certain tasks more than others     For many years  Fortran compilers existed which could do black magic to your numeric routines  making many important computations insanely fast   The contemporary C compilers couldn t do it as well   As a result  a number of great libraries of code grew in Fortran   If you want to use these well tested  mature  wonderful libraries  you break out the Fortran compiler   My informal observations show that these days people code their heavy computational stuff in any old language  and if it takes a while they find time on some cheap compute cluster   Moore s Law makes fools of us all

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I haven t heard that Fortan is significantly faster than C  but it might be conceivable tht in certain cases it would be faster  And the key is not in the language features that are present  but in those that  usually  absent    An example are C pointers  C pointers are used pretty much everywhere  but the problem with pointers is that the compiler usually can t tell if they re pointing to the different parts of the same array   For example if you wrote a strcpy routine that looked like this   strcpy char  d  const char  s      while  d      s         The compiler has to work under the assumption that the d and s might be overlapping arrays  So it can t perform an optimization that would produce different results when the arrays overlap  As you d expect  this considerably restricts the kind of optimizations that can be performed     I should note that C99 has a  restrict  keyword that explictly tells the compilers that the pointers don t overlap  Also note that the Fortran too has pointers  with semantics different from those of C  but the pointers aren t ubiquitous as in C    But coming back to the C vs  Fortran issue  it is conceivable that a Fortran compiler is able to perform some optimizations that might not be possible for a  straightforwardly written  C program  So I wouldn t be too surprised by the claim  However  I do expect that the performance difference wouldn t be all that much    5-10

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Generally FORTRAN is slower than C   C can use hardware level pointers allowing the programmer to hand-optimize   FORTRAN  in most cases  doesn t have access to hardware memory addressing hacks    VAX FORTRAN is another story     I ve used FORTRAN on and off since the  70 s    Really    However  starting in the 90 s FORTRAN has evolved to include specific language constructs that can be optimized into inherently parallel algorithms that can really scream on a multi-core processor    For example  automatic Vectorizing allows multiple processors to handle each element in a vector of data concurrently   16 processors -- 16 element vector -- processing takes 1 16th the time   In C  you have to manage your own threads and design your algorithm carefully for multi-processing  and then use a bunch of API calls to make sure that the parallelism happens properly   In FORTRAN  you only have to design your algorithm carefully for multi-processing   The compiler and run-time can handle the rest for you   You can read a little about High Performance Fortran  but you find a lot of dead links   You re better off reading about Parallel Programming  like OpenMP org  and how FORTRAN supports that

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To some extent Fortran has been designed keeping compiler optimization in mind  The language supports whole array operations where compilers can exploit parallelism  specially on multi-core processors   For example   Dense matrix multiplication is simply   matmul a b    L2 norm of a vector x is   sqrt sum x  2     Moreover statements such as FORALL  PURE  amp  ELEMENTAL procedures etc  further help to optimize code  Even pointers in Fortran arent as flexible as C because of this simple reason   The upcoming Fortran standard  2008  has co-arrays which allows you to easily write parallel code  G95  open source  and compilers from CRAY already support it    So yes Fortran can be fast simply because compilers can optimize parallelize it better than C C    But again like everything else in life there are good compilers and bad compilers

[c] Is Fortran easier to optimize than C for heavy calculations?

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