How to plot vectors in python using matplotlib

Question

I am taking a course on linear algebra and I want to visualize the vectors in action  such as vector addition  normal vector  so on    For instance    V   np array   1 1   -2 2   4 -7      In this case I want to plot 3 vectors V1    1 1   M2    -2 2   M3    4 -7    Then I should be able to add V1 V2 to plot a new vector V12 all together in one figure    when I use the following code  the plot is not as intended  import numpy as np import matplotlib pyplot as plt M   np array   1 1   -2 2   4 -7     print  vector 1   print M 0       print  vector 2     print M 1     rows cols   M T shape print cols   for i l in enumerate range 0 cols        print  Iteration    -    format i l       print  vector     format i       print M i         v1    0 0   M i 0  M i 1         v1    M i 0    M i 1       print v1      plt figure i      plt plot v1      plt show

User · Answer

What did you expect the following to do   v1    0 0   M i 0  M i 1   v1    M i 0    M i 1     This is making two different tuples  and you overwrite what you did the first time    Anyway  matplotlib does not understand what a  vector  is in the sense you are using  You have to be explicit  and plot  arrows    In  5   ax   plt axes    In  6   ax arrow 0  0   v1  head width 0 05  head length 0 1  Out 6    lt matplotlib patches FancyArrow at 0x114fc8358 gt   In  7   ax arrow 0  0   v2  head width 0 05  head length 0 1  Out 7    lt matplotlib patches FancyArrow at 0x115bb1470 gt   In  8   plt ylim -5 5  Out 8    -5  5   In  9   plt xlim -5 5  Out 9    -5  5   In  10   plt show     Result

User · Answer

In order to match the vector lenght and angle with the x y coordinates of the plot  you can use to following options to plt quiver  plt figure figsize  5 2   dpi 100  plt quiver 0 0 250 100  angles  xy   scale units  xy   scale 1  plt xlim 0 250  plt ylim 0 100

User · Answer

All nice solutions  borrowing and improvising for special case -  If you want to add a label near the arrowhead        arr    2 3      txt      Vector X        ax annotate txt  arr      ax arrow 0  0   arr  head width 0 05  head length 0 1

User · Answer

This may also be achieved using matplotlib pyplot quiver  as noted in the linked answer   plt quiver  0  0  0    0  0  0    1  -2  4    1  2  -7   angles  xy   scale units  xy   scale 1  plt xlim -10  10  plt ylim -10  10  plt show

User · Answer

How about something like import numpy as np import matplotlib pyplot as plt  V   np array   1 1    -2 2    4 -7    origin   np array   0  0  0   0  0  0      origin point  plt quiver  origin  V   0   V   1   color   r   b   g    scale 21  plt show     Then to add up any two vectors and plot them to the same figure  do so before you call plt show    Something like  plt quiver  origin  V   0   V   1   color   r   b   g    scale 21  v12   V 0    V 1    adding up the 1st  red  and 2nd  blue  vectors plt quiver  origin  v12 0   v12 1   plt show     NOTE  in Python2 use origin 0   origin 1  instead of  origin

User · Answer

Thanks to everyone  each of your posts helped me a lot   rbierman code was pretty straight for my question  I have modified a bit and created a function to plot vectors from given arrays  I d love to see any suggestions to improve it further    import numpy as np import matplotlib pyplot as plt def plotv M       rows cols   M T shape     print rows cols        Get absolute maxes for axis ranges to center origin      This is optional     maxes   1 1 np amax abs M   axis   0      colors     b   r   k       fig   plt figure       fig suptitle  Vectors   fontsize 10  fontweight  bold        ax   fig add subplot 111      fig subplots adjust top 0 85      ax set title  Vector operations        ax set xlabel  x       ax set ylabel  y        for i l in enumerate range 0 cols              print i          plt axes   arrow 0 0 M i 0  M i 1  head width 0 2 head length 0 1 zorder 3           ax text M i 0  M i 1   str M i    style  italic               bbox   facecolor   red    alpha  0 5   pad  0 5        plt plot 0 0  ok     lt -- plot a black point at the origin       plt axis  equal      lt -- set the axes to the same scale     plt xlim  -maxes 0  maxes 0      lt -- set the x axis limits     plt ylim  -maxes 1  maxes 1      lt -- set the y axis limits      plt grid b True  which  major     lt -- plot grid lines     plt show    r   np random randint 4 size  2 2   print r 0     print r 1     r12   np add r 0    r 1     print r12  plotv np vstack  r r12      Vector addition performed on random vectors

User · Answer

Your main problem is you create new figures in your loop  so each vector gets drawn on a different figure  Here s what I came up with  let me know if it s still not what you expect   CODE   import numpy as np import matplotlib pyplot as plt M   np array   1 1   -2 2   4 -7     rows cols   M T shape   Get absolute maxes for axis ranges to center origin  This is optional maxes   1 1 np amax abs M   axis   0   for i l in enumerate range 0 cols        xs    0 M i 0       ys    0 M i 1       plt plot xs ys   plt plot 0 0  ok     lt -- plot a black point at the origin plt axis  equal      lt -- set the axes to the same scale plt xlim  -maxes 0  maxes 0      lt -- set the x axis limits plt ylim  -maxes 1  maxes 1      lt -- set the y axis limits plt legend   V  str i 1  for i in range cols      lt -- give a legend plt grid b True  which  major     lt -- plot grid lines plt show     OUTPUT     EDIT CODE   import numpy as np import matplotlib pyplot as plt M   np array   1 1   -2 2   4 -7     rows cols   M T shape   Get absolute maxes for axis ranges to center origin  This is optional maxes   1 1 np amax abs M   axis   0  colors     b   r   k     for i l in enumerate range 0 cols        plt axes   arrow 0 0 M i 0  M i 1  head width 0 05 head length 0 1 color   colors i    plt plot 0 0  ok     lt -- plot a black point at the origin plt axis  equal      lt -- set the axes to the same scale plt xlim  -maxes 0  maxes 0      lt -- set the x axis limits plt ylim  -maxes 1  maxes 1      lt -- set the y axis limits plt grid b True  which  major     lt -- plot grid lines plt show     EDIT OUTPUT

[python] How to plot vectors in python using matplotlib

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