how can i plot contour

i encounter an error while trying to plot the following contour

x=0:0.1:4;
x1=-pi:0.001*pi:pi;
y1=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.-sin(x1/2.).*sin(3.*x1/2.));
y2=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.+sin(x1/2.).*sin(3.*x1/2.));
y3=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*sin(x1/2.).*sin(3.*x1/2.);
y4=(1/2).*((y1-y2)^2+y1^2+y2^2+6.*y3^2);
z=abs(sqrt(y4));
[x,x1]=meshgrid(x,x1);
% contour(x,x1,z)
contour(real(z))

Answer 1

[Walter Roberson]

x = (0:0.1:4).';
x1=-pi:0.001*pi:pi;
y1=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.-sin(x1/2.).*sin(3.*x1/2.));
y2=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.+sin(x1/2.).*sin(3.*x1/2.));
y3=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*sin(x1/2.).*sin(3.*x1/2.);
y4 = (1/2).*((y1-y2).^2+y1.^2+y2.^2+6.*y3);
z = sqrt(y4);
[x,y]=meshgrid(x1,x);
% contour(x,x1,z)
contour(x, y, real(z))

[khaled Abdelghafar]

x = (0:0.1:4).';
x1=-pi:0.001*pi:pi;
x2=x.*cos(x1);
x3=x.*sin(x1);
y1=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.-sin(x1/2.).*sin(3.*x1/2.));
y2=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*(1.+sin(x1/2.).*sin(3.*x1/2.));
y3=(100*sqrt(2*pi)./sqrt(x.*2*pi)).*cos(x1/2).*sin(x1/2.).*sin(3.*x1/2.);
y4 = (1/2).*((y1-y2).^2+y1.^2+y2.^2+6.*y3.^2);
z = sqrt(y4);
[x,y]=meshgrid(x2,x3);

Error using repmat
Requested 82041x82041 (50.1GB) array exceeds maximum array size preference (30.9GB). This might cause MATLAB to become unresponsive.

Error in meshgrid (line 61)
xx = repmat(xrow,size(ycol));

% contour(x2,x3,z)
contour(x, y, real(z),'ShowText','on')

what is the error in this code

i want to plot contours in x, y not r and Theta

[Walter Roberson]

x = (0:0.1:4).';
x1=-pi:0.001*pi:pi;
x2=x.*cos(x1);
x3=x.*sin(x1);
whos

  Name       Size               Bytes  Class     Attributes

  x         41x1                  328  double              
  x1         1x2001             16008  double              
  x2        41x2001            656328  double              
  x3        41x2001            656328  double              

Notice your x2 and x3 are 41 x 2001, not vectors. You are combining a vector of length 41 with a vector of length 2001. In order to get a vector result, you would need to reduce along a dimension (such as min or sum) to get either 41 x 1 or 1 x 2001.

[x,y]=meshgrid(x2,x3);

There you are asking to use the 41x2001 array x2 in combination with each 41x2001 x3 value, which is 82041 x 82041 requested, which is too big for your system.

i want to plot contours in x, y not r and Theta

x1 is plausibly an angle, maybe even Theta; why not name it Theta instead of x1 ?

x is... we don't know? Is that your r?

[khaled Abdelghafar]

yes r is x

theta is x1

[khaled Abdelghafar]

i would changed to r and theta

the question how i plot the contour in x,y not r and thata

how could i do it

[Walter Roberson]

https://www.mathworks.com/matlabcentral/fileexchange/14826-polar-contour-plot

You do not need to construct x2 and x3 for that contribution.