MATLAB Answers


Index exceeds matrix dimensions.

Asked by Sara
on 20 Jun 2012

for the code below I received the error index exceeds.. I do not know how can I fix it.

x = zeros( 2,length(v0) ) ;  
for k = 1:length(v0)
  A = [ factor1(:,k) factor2(:,k)];
  b = -rhs(:,k);
  x(:,k) = A\b ;
//end of for     

length v0 = 2501

A\b is 2 by 2 matrix but x(:,k) is 2 by 2501.


Which line is generating the error?

What are the sizes of factor1 and factor2 and rhs ?

on 20 Jun 2012

the sizes of factor1 and factor2 are 2 by 2501.
by the line x (:,k) = A\b , it has error.

That doesn't sound like an "index exceeds" error, that sounds like an error about RHS having more non-singleton dimensions than the LHS has.

Please show the exact error.

If A\b is a 2 x 2 matrix, then were you only expecting a 2 x 1 matrix as the result of the A\b operation? Or you only care about one of the rows or one of the columns? Or you want to store all 4 results and do that in a single column ?


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1 Answer

Answer by per isakson
on 20 Jun 2012

Do you use the debugger?

  1. Put a break on the line that causes the error or
  2. Tools | Debug | Stop if Error
  3. Run the code
  4. At the break inspect the values of the index


A zero index would generate the error about indices needing to be positive integers, not the error about exceeding matrix dimensions.

Thanks Walter; fixed. I try to make the point that better asking the debugger than Answer.

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