vertical horizontal lines in matplotlib

Question

I do not quite understand why I am unable to create horizontal and vertical lines at specified limits  I would like to bound the data by this box  However  the sides do not seem to comply with my instructions  Why is this      CREATING A BOUNDING BOX   BOTTOM HORIZONTAL plt axhline y  4  xmin 0 25  xmax 0 402  linewidth 2  color    k     RIGHT VERTICAL plt axvline x 0 402  ymin 0 4  ymax   0 615  linewidth 2  color  k     LEFT VERTICAL plt axvline x 0 1  ymin 0 58  ymax   0 79  linewidth 2  color  k   plt show

User · Accepted Answer

The pyplot functions you are calling  axhline   and axvline   draw lines that span a portion of the axis range  regardless of coordinates  The parameters xmin or ymin use value 0 0 as the minimum of the axis and 1 0 as the maximum of the axis   Instead  use plt plot  x1  x2    y1  y2    k-   to draw a line from the point  x1  y1  to the point  x2  y2  in color k  See pyplot plot

User · Answer

If you want to add a bounding box  use a rectangle   ax   plt gca   r   matplotlib patches Rectangle   5   5    25   1  fill False  ax add artist r    Rectangle doc

User · Answer

This may be a common problem for new users of Matplotlib to draw vertical and horizontal lines  In order to understand this problem  you should be aware that different coordinate systems exist in Matplotlib    The method axhline and axvline are used to draw lines at the axes coordinate  In this coordinate system  coordinate for the bottom left point is  0 0   while the coordinate for the top right point is  1 1   regardless of the data range of your plot  Both the parameter xmin and xmax are in the range  0 1    On the other hand  method hlines and vlines are used to draw lines at the data coordinate  The range for xmin and xmax are the in the range of data limit of x axis   Let s take a concrete example    import matplotlib pyplot as plt import numpy as np  x   np linspace 0  5  100  y   np sin x   fig  ax   plt subplots    ax plot x  y  ax axhline y 0 5  xmin 0 0  xmax 1 0  color  r   ax hlines y 0 6  xmin 0 0  xmax 1 0  color  b    plt show     It will produce the following plot    The value for xmin and xmax are the same for the axhline and hlines method  But the length of produced line is different

[matplotlib] vertical & horizontal lines in matplotlib

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