Magnetic Field Contour: 0.2-1, -3 to 3

[omiros]

Hello everyone,

I am struggling a bit with a Matlab program that I am writing. I am supposed to create a contour of the magnitude of the magnetic field, in and out of a wire. Basically the function is

|B| = r for -1≤r≤ 1 and |B| = 1/r for -3≤r≤-1 & 1≤r≤3
where r is the radius

However the contour that I have to plot is for |B| from 0.2 to 1 with steps of 0.2 (0.2, 0.4, 0.6, 0.8, 1.0) and it also has to be in Cartesian coordinates x,y both from -3 to 3.

What I've gotten so far is :

[phii,rhoi]=meshgrid(-pi:0.05*pi:pi,-1:0.05:1);
[x,y]=pol2cart(phii,rhoi);
B1 = sqrt(x.^2+y.^2);
(for inside the wire)

rhoo=[-3:0.1:-1,1:0.1:3];
phio=[-pi:0.05*pi:pi];
[phio,rhoo]=meshgrid(phio,rhoo);
[x1,y1]=pol2cart(phio,rhoo);
B2 = 1./(sqrt((x1).^2+(y1).^2));
(outside the wire)

figure(3);
hold all;
contour(x,y,B1);
contour(x1,y1,B2);
hold off;

In conclusion my problem is how to limit both B1 and B2 for value only equals to the ones above.

 

[Future Bruno]

Thank you for your help!</code>Here is the solution I got:[phii,rhoi]=meshgrid(-pi:0.05*pi:pi,-1:0.05:1);[x,y]=pol2cart(phii,rhoi);B1 = sqrt(x.^2+y.^2);rhoo=[-3:0.1:-1,1:0.1:3];phio=[-pi:0.05*pi:pi];[phio,rhoo]=meshgrid(phio,rhoo);[x1,y1]=pol2cart(phio,rhoo);B2 = 1./(sqrt((x1).^2+(y1).^2));%create a matrix to store the values of B that are within the rangeB1_matrix = zeros(size(B1));B2_matrix = zeros(size(B2));for i=1:length(B1) for j=1:length(B1) if B1(i,j) >= 0.2 && B1(i,j) <= 1 B1_matrix(i,j) = B1(i,j); end endendfor i=1:length(B2) for j=1:length(B2) if B2(i,j) >= 0.2 && B2(i,j) <= 1 B2_matrix(i,j) = B2(i,j); end endendfigure(3);hold all;contour(x,y,B1_matrix);contour(x1,y1,B2_matrix);hold off;