How to solve it for a scalar output?

Hi,

I'm trying to find the electron current using the relation J=sigma[E+uxB]

for which my code gives an error

Unable to perform assignment because the left and right sides have a different number of elements.

Error in pde2fshear_fisher_new>pdex2pde (line 738)

je(STEP_x)=sig*(DuDx(1)+cross(ue,Bt));

which I'm unable to debug it

my code is as below

            
           function [c,f,s] = pdex2pde(x,t,u,DuDx)
           c = [1;1;1];STEP_x=2; zone=1;B0=4617;a=.9;R0=6; ue = [1.0;0;0];
            xmin = 0;xmax = 1;xstep = 100; sig=1;
           X = linspace(xmin,xmax,xstep-1);
           if STEP_x==1 
            Btx=B0/(R0/a+zone*X(STEP_x));
            Bt=[Btx;0;0];
            je(STEP_x)= sig*(DuDx(1)+cross(ue,Bt));
                    
            elseif STEP_x > 1  && STEP_x <= 5  
            Btx=B0/(R0/a+zone*X(STEP_x));
            disp(Btx);
            Bt=[Btx;0;0];
            je(STEP_x)=sig*(DuDx(1)+cross(ue,Bt));
            
            else
            Btx=B0/(R0/a+zone*X(STEP_x));
            Bt=[Btx;0;0];
            je(STEP_x)=sig*(DuDx(1)+cross(ue,Bt));
            
            end
           end

Answer 1

[Torsten]

cross(...) usually gives a vector as result, but je(STEP_x) is a scalar. You can't assign a vector to a scalar.

a(1) = cross([1 2 3],[4 5 6])

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

[Rahul]

Fine. I accept.

But if I take norm of the RHS, it is possible.

But I wonder if it make sense or not?

[Walter Roberson]

            je(STEP_x) = sig*(DuDx(1) + norm(cross(ue,Bt)));

Question:

What is the difference between your three branches? The only difference I can see is that you have an extra disp(Btx); in one of the branches.

[Torsten]

But I wonder if it make sense or not?

I wonder how I could tell.