I'm writing Webwork problems whose solutions are matrices whose entries are variables (but not algebraic expressions in the variables), like e, x_0, x_1, ..., x_n.

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(1) How do I handle subscripts? I tried

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$ans1 = Compute("x0")->reduce();

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ANS($ans1->cmp());

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but Webwork treats it as x*0, which is not good.

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(2) The matrices have fixed size, say 4x4. Is it possible to store the students' input as entries of a 2-dimensional array as oppose to 16 different variables? (e.g a[1][1], a[1][2], etc)

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(3) Assuming that I can store the student input as an array a[i][j], is it possible to check the answer by running through a loop? e.g. to check that it is symmetric I would do something like this:

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flag=1;

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for i=2 to n

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for j=1 to n-1

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if a[i][j] != a[j][i] then flag=0;

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end;

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end;

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if flag==0 then CORRECT else WRONG

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(this is just an example; I need to check something more complicated)

MANY THANKS!