Matrix multiplication using arrays

Question

I m trying to make a simple matrix multiplication method using multidimensional arrays   2  2    I m kinda new at this  and I just can t find what it is I m doing wrong  I d really appreciate any help in telling me what it is  I d rather not use libraries or anything like that  I m mostly doing this to learn how it works  Thank you so much in advance   I m declaring my arays in the main method as follows   Double     A   4 00 3 00   2 00 1 00     Double     B   -0 500 1 500   1 000 -2 0000      A B should return the identity matrix  It doesn t   public static Double     multiplicar Double     A  Double     B     the method runs and returns a matrix of the correct dimensions    I actually changed the  length function to a specific value to eliminate    it as a possible issue   but not the correct values      Double     C  new Double 2  2       int i j           I fill the matrix with zeroes  if I don t do this it gives me an error     for i 0 i lt 2 i              for j 0 j lt 2 j                 C i  j  0 00000                          this is where I m supposed to perform the adding of every element in       a row of A multiplied by the corresponding element in the       corresponding column of B  for all columns in B and all rows in A     for i 0 i lt 2 i             for j 0 j lt 2 j                C i  j    A i  j  B j  i              return C

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static int b       21 21   22 22     static int a        1 1   2 2     public static void mul        int c       new int 2  2        for int i 0 i lt b length i             for int j 0 j lt b length j                 c i  j   0                          for int i 0 i lt a length i             for int j 0 j lt b length j                 for int k 0 k lt b length k                 c i  j   c i  j    a i  k    b k  j                                       for int i 0 i lt c length i             for int j 0 j lt c length j                 System out print c i  j                         System out println   n

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My code is super easy and works for any order of matrix public static void main String   args        Scanner sc   new Scanner System in       System out println  quot  Enter No  of rows in matrix 1    quot        int arows   sc nextInt        System out println  quot  Enter No  of columns in matrix 1    quot        int acols   sc nextInt        System out println  quot  Enter No  of rows in matrix 2    quot        int brows   sc nextInt        System out println  quot  Enter No  of columns in matrix 2    quot        int bcols   sc nextInt        if  acols    brows            System out println  quot  Enter elements of matrix 1  quot            int a       new int arows  acols           int b       new int brows  bcols           for  int i   0  i  lt  arows  i                  for  int j   0  j  lt  acols  j                      a i  j    sc nextInt                                    System out println  quot  Enter elements of matrix 2  quot            for  int i   0  i  lt  brows  i                  for  int j   0  j  lt  bcols  j                      b i  j    sc nextInt                                    System out println  quot  The Multiplied matrix is    quot            int sum   0          int c       new int arows  bcols           for  int i   0  i  lt  arows  i                  for  int j   0  j  lt  bcols  j                      for  int k   0  k  lt  brows  k                          sum   sum   a i  k    b k  j                       c i  j    sum                                     System out print c i  j     quot   quot                    sum   0                            System out println                    else           System out println  quot Order of matrix in invalid quot

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import java util    public class Mult    public static int     C   public static void main String   args         Scanner s   new Scanner System in        System out println  Enter Row of Matrix A        int Rowa   s nextInt         System out println  Enter Column of Matrix A        int Cola   s nextInt         System out println  Enter Row of Matrix B        int Rowb   s nextInt         System out println  Enter Column of Matrix B        int Colb   s nextInt         int     A   new int Rowa  Cola       int     B   new int Rowb  Colb        C  new int Rowa  Colb         int     C   new int      System out println  Enter Values of Matrix A         for int i  0   i lt  A length   i              for int j   0   j lt A length j                  A i  j    s nextInt                          System out println  Enter Values of Matrix B         for int i  0   i lt  B length   i              for int j   0   j lt B length j                  B i  j    s nextInt                            if Cola  Rowb            for int i   0 i  lt  A length i                   for int j   0 j  lt  A length j                      C i  j  0                   for int k   0 k  lt  B length k                         C i  j     A i  k    B k  j                                                             else           System out println  Cannot multiply                          Printing matrix A            for int i  0   i lt  A length   i              for int j   0   j lt A length j              System out print A i  j     t                      System out println                      for int i  0   i lt  A length   i              for int j   0   j lt A length j              System out print C i  j     t                      System out println

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Java  Matrix multiplication   Tested with matrices of different size   public class Matrix           Matrix multiplication method      param m1 Multiplicand     param m2 Multiplier     return Product         public static double     multiplyByMatrix double     m1  double     m2            int m1ColLength   m1 0  length     m1 columns length         int m2RowLength   m2 length        m2 rows length         if m1ColLength    m2RowLength  return null     matrix multiplication is not possible         int mRRowLength   m1 length        m result rows length         int mRColLength   m2 0  length     m result columns length         double     mResult   new double mRRowLength  mRColLength           for int i   0  i  lt  mRRowLength  i                 rows from m1             for int j   0  j  lt  mRColLength  j             columns from m2                 for int k   0  k  lt  m1ColLength  k         columns from m1                     mResult i  j     m1 i  k    m2 k  j                                                     return mResult             public static String toString double     m            String result               for int i   0  i  lt  m length  i                  for int j   0  j  lt  m i  length  j                      result    String format   11 2f   m i  j                              result      n                     return result             public static void main String   args                1         double     multiplicand   new double                        3  -1  2                    2   0  1                    1   2  1                     double     multiplier   new double                        2  -1  1                    0  -2  3                    3   0  1                     System out println   1 n    toString multiplyByMatrix multiplicand  multiplier                 2         multiplicand   new double                        1  2  0                    -1  3  1                    2  -2  1                     multiplier   new double                        2                    -1                    1                     System out println   2 n    toString multiplyByMatrix multiplicand  multiplier                 3         multiplicand   new double                        1  2  -1                    0   1  0                     multiplier   new double                        1  1  0  0                    0  2  1  1                    1  1  2  2                     System out println   3 n    toString multiplyByMatrix multiplicand  multiplier               Output    1       12 00      -1 00       2 00        7 00      -2 00       3 00        5 00      -5 00       8 00   2        0 00       -4 00        7 00   3        0 00       4 00       0 00       0 00        0 00       2 00       1 00       1 00

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try this it may help you  import java util Scanner   public class MulTwoArray    public static void main String   args         int i  j  k      int     a   new int 3  3       int     b   new int 3  3       int     c   new int 3  3          Scanner sc   new Scanner System in        System out println  Enter size of array a        int rowa   sc nextInt        int cola   sc nextInt         System out println  Enter size of array b        int rowb   sc nextInt        int colb   sc nextInt            read and b      System out println  Enter elements of array a        for  i   0  i  lt  rowa    i            for  j   0  j  lt  cola    j                 a i  j    sc nextInt                       System out println              System out println  Enter elements of array b        for  i   0  i  lt  rowb    i            for  j   0  j  lt  colb    j                 b i  j    sc nextInt                       System out println   n                 print a and b      System out println  the elements of array a        for  i   0  i  lt  rowa    i            for  j   0  j  lt  cola    j                 System out print a i  j                System out print   t                       System out println   n              System out println  the elements of array b        for  i   0  i  lt  rowb    i            for  j   0  j  lt  colb    j                 System out print b i  j                System out print   t                       System out println   n                  multiply a and b      for  i   0  i  lt  rowa    i             for  j   0  j  lt  colb    j                c i  j    0              for  k   0  k  lt  cola    k                    c i  j     a i  k    b k  j                                         print multi result      System out println  result of multiplication of array a and b is         for  i   0  i  lt  rowa    i            for  j   0  j  lt  colb    j                 System out print c i  j                System out print   t                      System out println   n

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Try this   public static Double     multiplicar Double A     Double B           Double     C  new Double 2  2       int i j k       for  i   0  i  lt  2  i               for  j   0  j  lt  2  j                   C i  j    0 00000                        for i 0 i lt 2 i             for j 0 j lt 2 j                 for  k 0 k lt 2 k                       C i  j    A i  k  B k  j                                        return C

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You can try this code   public class MyMatrix       Double     A       4 00  3 00      2 00  1 00          Double     B       -0 500  1 500      1 000  -2 0000           public static Double     multiplicar Double     A  Double     B             int aRows   A length          int aColumns   A 0  length          int bRows   B length          int bColumns   B 0  length           if  aColumns    bRows                throw new IllegalArgumentException  A Rows      aColumns     did not match B Columns     bRows                            Double     C   new Double aRows  bColumns           for  int i   0  i  lt  aRows  i                  for  int j   0  j  lt  bColumns  j                      C i  j    0 00000                                   for  int i   0  i  lt  aRows  i         aRow             for  int j   0  j  lt  bColumns  j         bColumn                 for  int k   0  k  lt  aColumns  k         aColumn                     C i  j     A i  k    B k  j                                                      return C             public static void main String   args             MyMatrix matrix   new MyMatrix            Double     result   multiplicar matrix A  matrix B            for  int i   0  i  lt  2  i                  for  int j   0  j  lt  2  j                    System out print result i  j                      System out println

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The method mults is a procedure Pascal  or subroutine Fortran   The method multMatrix is a function Pascal Fortran   import java util     public class MatmultE   private static Scanner sc   new Scanner System in     public static void main String    args          double     A   4 00 3 00   2 00 1 00         double     B   -0 500 1 500   1 000 -2 0000        double     C multMatrix A B       printMatrix A       printMatrix B           printMatrix C        double a         1  2  -2  0    -3  4  7  2    6  0  3  1        double b         -1  3    0  9    1  -11    4  -5        double     c multMatrix a b       printMatrix a       printMatrix b           printMatrix c        double     a1   readMatrix        double     b1   readMatrix        double     c1   new double a1 length  b1 0  length       mults a1 b1 c1 a1 length a1 0  length b1 length b1 0  length       printMatrix c1       printMatrixE c1           public static double     readMatrix            int rows   sc nextInt           int cols   sc nextInt           double     result   new double rows  cols          for  int i   0  i  lt  rows  i                 for  int j   0  j  lt  cols  j                    result i  j    sc nextDouble                                 return result           public static void printMatrix double     mat      System out println  Matrix   mat length      mat 0  length              int rows   mat length         int columns   mat 0  length         for  int i   0  i  lt  rows  i                 for  int j   0  j  lt  columns  j                     System out printf   8 3f     mat i  j                            System out println                System out println           public static void printMatrixE double     mat      System out println  Matrix   mat length      mat 0  length              int rows   mat length         int columns   mat 0  length         for  int i   0  i  lt  rows  i                 for  int j   0  j  lt  columns  j                     System out printf   9 2e     mat i  j                            System out println                System out println             public static double     multMatrix double a      double b        a m  n   b n  p     if a length    0  return new double 0  0      if a 0  length    b length  return null    invalid dims     int n   a 0  length     int m   a length     int p   b 0  length      double ans       new double m  p       for int i   0 i  lt  m i           for int j   0 j  lt  p j              ans i  j  0           for int k   0 k  lt  n k                 ans i  j     a i  k    b k  j                              return ans           public static void mults double a      double b      double c      int r1                           int c1  int r2  int c2         for int i   0 i  lt  r1 i              for int j   0 j  lt  c2 j                 c i  j  0              for int k   0 k  lt  c1 k                    c i  j     a i  k    b k  j                                             where as input matrix you can enter   inE txt  4 4 1 1 1 1 2 4 8 16 3 9 27 81 4 16 64 256 4 3 4 0 -3 0 4 0 -13 0 19 0 -7 0 3 0 -2 0 7 0 -1 0 1 0 -1 0   in unix like cmmd line execute the command     java MatmultE  lt  inE txt   outE txt  and you get the output  outC txt  Matrix 2  2     4 000    3 000     2 000    1 000   Matrix 2  2    -0 500    1 500     1 000   -2 000   Matrix 2  2     1 000    0 000     0 000    1 000   Matrix 3  4     1 000    2 000   -2 000    0 000    -3 000    4 000    7 000    2 000     6 000    0 000    3 000    1 000   Matrix 4  2    -1 000    3 000     0 000    9 000     1 000  -11 000     4 000   -5 000   Matrix 3  2    -3 000   43 000    18 000  -60 000     1 000  -20 000   Matrix 4  3    -7 000   15 000    3 000   -36 000   70 000   20 000  -105 000  189 000   57 000  -256 000  420 000   96 000   Matrix 4  3  -7 00e 00  1 50e 01  3 00e 00  -3 60e 01  7 00e 01  2 00e 01  -1 05e 02  1 89e 02  5 70e 01  -2 56e 02  4 20e 02  9 60e 01

[java] Matrix multiplication using arrays

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