Subscripted assignment dimension mismatch.

Whats going wrong and how can I fix this?

Getting "error Subscripted assignment dimension mismatch.

Error in Untitled (line 10)"

Code:

x1=linspace(0,1,100);

t=linspace(0,4,400);

for i=1:length(x1);

      for j=1:length(t);
        u(i,j)=0;
        cn=0;
          for n=1:400;
              cn=2/(pi*n)*(1-2*(1-2*cos(pi*n))/((pi*n)^2+4));
              u(i,j)=u(i,j)+(cn*exp(-(pi*n)^2*t)+2/(pi*n)*(1-2*cos(pi*n))/((pi*n)^2+4)*(2*cos(2*t)-(pi*n)^2*sin(2*t)))*sin(pi*n*x1(i));
          end
      end
  end

Answer 1

[Adam]

Try splitting your maths into multiple statements to check each part more easily when you get problems like this.

You set

u(i,j) = 0;

in your for loop, but first time round that means u is just a scalar, but all the stuff you add to it later on is a 1x400 array. You can't add a 1x400 array to u(i,j) like that. I'm not sure what you actually intended, but t is vectorised so looping round it also with j doesn't seem right.

Answer 2

[Star Strider]

Not really certain what you intend, but since ‘t’ has 400 elements and your ‘n’ loop the same, I assume you intend to have a value of ‘t’ for each iteration. You may need to subscript ‘t’ as ‘t(n)’.

See if changing to this line improves things:

u(i,j)=u(i,j)+(cn*exp(-(pi*n)^2*t(n))+2/(pi*n)*(1-2*cos(pi*n))/((pi*n)^2+4)*(2*cos(2*t(n))-(pi*n)^2*sin(2*t(n))))*sin(pi*n*x1(i));