# How to plot a polar plot from a matrix or excel file ?

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Anshuman S on 12 Oct 2018
Commented: Walter Roberson on 12 Oct 2018
I have a matrix A which contains values at different angles & radius. The index of this matrix represents ( angles,radius ) as (i,j) . Now how to plot these values on a polar plot ? I also want to make a contour plot for these values in polar co-ordinate .
Let the matrix be test file ( analytical.csv) attached with this document. It contains 5 columns and 4 rows , colums represent different radius = ( 0 , 0.25, 0.50 , 0.75 , 1 ) and rows represent different angles = ( 0 , pi/2 , pi , 3pi/2 ) respectively.
Thanks

Anshuman S on 12 Oct 2018
if true
m = input ('M in multiple of 4*2^r ');
n = input ('N in n+1 taking 0 as well , e.g 5 ');
sol= zeros(m,n);
s=0;
for j = 1:n
for i = 1:m
r = 0.03*(j-1)*(1/(n-1)) ;
fi = 2*pi*(i-1)/(m) ;
%disp(r)
%disp(fi)
%disp('r,fi')
for m1 =1:10000
s = s + (2*cos(2*m1*fi)*((r/0.03)^(2*m1))) / ((4*m1*m1 - 1)*(1 +
(2*m1*45)/(20*0.03)));
%disp(s)
end
A(i,j)= (1353/20)*(1/pi - (s/pi) + ((r/0.03)*sin(fi))/(2*(1+
(45/(20*0.03)))));
end
end
%filename = 'analytical1';
%xlswrite(filename,sol)
r = [ 0 , 0.25, 0.50 , 0.75 , 1] ;
th = [ 0 , pi/2 , pi , 3*pi/2 ] ;
[R,T] = meshgrid(r,th) ;
% Create polar data
% Convert to Cartesian
X = R.*cos(T);
Y = R.*sin(T);
h = polar(X,Y);
hold on;
contourf(X,Y,A);
% Hide the POLAR function data and leave annotations
set(h,'Visible','off')
% Turn off axes and set square aspect ratio
axis off
axis image
%disp(sol)
% code
end
Anshuman S on 12 Oct 2018
take m = 4 and n = 5
Star Strider on 12 Oct 2018

KSSV on 12 Oct 2018
r = [ 0 , 0.25, 0.50 , 0.75 , 1] ;
th = [ 0 , pi/2 , pi , 3*pi/2 ] ;
[R,T] = meshgrid(r,th) ;
% Create polar data
% Convert to Cartesian
X = R.*cos(T);
Y = R.*sin(T);
h = polar(X,Y);
hold on;
contourf(X,Y,A);
% Hide the POLAR function data and leave annotations
set(h,'Visible','off')
% Turn off axes and set square aspect ratio
axis off
axis image

Anshuman S on 12 Oct 2018
I am not able to follow the instructions on my computer system, can you please help with the contour plot of this matrix which I am attaching with this comment.
The matrix is 64x8 , where 64 is number of points corresponding to phi angle and 8 is the points corresponding to radius. i.e for radius it's R = [0 1/8 2/8 3/8 4/8 5/8 6/8 7/8] similarly for phi [ 0 2pi/64 4pi/64 ...... 62pi/64 ].
Anshuman S on 12 Oct 2018
Walter Roberson on 12 Oct 2018
You have chosen to replace Mathwork's plot.m with your own. Because plot() is called in many places in MATLAB, you will need to upgrade your plot.m to handle all of those cases, which will take a lot of work.
What is it that you are extending plot() to be able to handle that it does not handle already ?
Because a partly-completed plot.m is likely to interfere with your use of MATLAB until you have completely finished your fully-compatible extension or replacement of plot(), we would recommend that you name your plot.m by some other name while you work through the development stages.
... We are not sure what any of this has to do with the task of drawing a contour plot of that matrix. Why not use the regular contour() call to do that instead of developing a complete replacement for plot() ?

Image Analyst on 12 Oct 2018
Do not call your m-file plot.m. Call it myPlot.m or something like that. Obviously change the name inside the file too.

#### 1 Comment

Walter Roberson on 12 Oct 2018
... and my https://www.mathworks.com/matlabcentral/answers/423580-how-to-plot-a-polar-plot-from-a-matrix-or-excel-file#comment_621408 describes why it is a problem to name your file plot.m if you are not deliberately replacing Mathwork's plot() function...