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octave

Problem with Octave. Can't recognize a matrix

I try to build a script on Octave and I receive this message:

error: script2: =: nonconformant arguments (op1 is 1x1, op2 is 1x10)
error: called from
    script2 at line 5 column 1

My script is:

l = 20:29;
m = 30;

for i = 0:9
  a(i + 1) = l / m;
end

Can someone help me fix this?

Solution

  • Octave allows you to assign to a non-existent name by making a scalar. You can then append to it by assigning to an index that is one past the length.

    When you assign to a(1), a is created as a scalar (or 1x1 array). l / m is 1x10. That is what your error message is telling you.

    There are a couple of workarounds. If you want to just accumulate the rows of a matrix, add a second dimension:

    a(i + 1, :) = l / m;

    If you want columns:

    a(:, i + 1) = l / m;

    The problem with this approach is that it reallocates the matrix at every iteration. The recommended approcach is to pre-allocate the matrix a and fill it in:

    l = 20:29;
m = 30;
a = zeros(10);

for i = 1:10
  a(i + 1, :) = l / m;
end