plot a function of 2 variables inside a for loop

I have this equation where A,B are onstants and E= ( 1-( ((1-B)/2.*J).*(1+(E.*J/(A*B)))*sqrt(E.*J.*A/B) ));

I need to plot E as J varies from 0:300 however when I evaluate E inside a for loop from 0:300 using solve command I get error in using indices. This is the piece of code:

A=5;
B=0.9;
J=0:300;
syms E J 
for i= 1:lenght(j)
 E(i)= solve(( 1-( ((1-B)/2.*J(i)).*(1+(E(i).*J(i)/(A*B)))*sqrt(E(i).*J(i).*A/B) )),J(i));
end

Answer 1

[Rik]

You are overwriting J and using j in your loop definition.

You should define an array to hold the result. Then you can define E as a symbolic variable. Since J has a definite value, it is not symbolic.

Also, don't use i or j as variable names and use numel or size instead of length.

The last change you need to make is to not index E. You could also use J directly in the for loop definition, but that is a matter of taste.

[Kim Ibrahim]

I have tried your comments and got : "Dimensions do not match error"

and the code:

A= 0.9;
B= 5;
J= 1:300;
E=[];
syms E 
for k=1:numel(J)
E=solve(( 1-( ((1-A)/2.*J).*(1+(E.*J/(A*B)))*sqrt(E.*J.*B/A) )),J);
end

[Kim Ibrahim]

and when I use indexing for both E and J i get "Unable to perform assignment because the left and right sides have a different number of elements."

[Rik]

A= 0.9;
B= 5;
J= 1:300;
E_sol=zeros(size(J));
syms E 

w=warning('off','symbolic:solve:PossiblySpuriousSolutions');
for k=1:numel(J)
    %You should solve for E, since you want to know the value of E
    tmp=solve(( 1-( ((1-B)/2.*J(k)).*(1+(E.*J(k)/(A*B)))*sqrt(E.*J(k).*A/B) )),E);
    if k==1,tmp,end %debug information
    tmp=double(tmp);
    if k==1,tmp,end %debug information
    
    %You probably want to select the real solution
    [imag_val,ind]=min(abs(imag(tmp)));
    if imag_val > 2*eps
        warning('J=%.0f did not return a real solution',J(k))
        E_sol(k)=NaN;
        continue
    end
    
    E_sol(k)=tmp(ind);
end

tmp = 

tmp = 
   0.9477 + 0.0000i
  -4.9738 - 2.2222i
  -4.9738 + 2.2222i

Warning: J=50 did not return a real solution

Warning: J=100 did not return a real solution

Warning: J=150 did not return a real solution

Warning: J=200 did not return a real solution

Warning: J=250 did not return a real solution

Warning: J=300 did not return a real solution

warning(w);%reset warning state
E_sol

E_sol = 1×300

0.9477 0.1523 0.0483 0.0209 0.0108 0.0063 0.0040 0.0027 0.0019 0.0014 0.0010 0.0008 0.0006 0.0005 0.0004 0.0003 0.0003 0.0002 0.0002 0.0002 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001