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I am completely new to Mathematics. I am doing an exercise which requires me to use Table to make a $10 \times 10$ matrix with numbers $1,2,...,10$ on the diagonal and $1$ in the upper diagonal entries and with $0$ in the lower diagonal matrix.

I have been able to generate the diagonal command along with the upper diagonal command (using If) but that yields $1$ in the lower diagonals also.

Can anybody help me with this code?

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  • $\begingroup$ Show us the code please. $\endgroup$ – Kuba♦ Apr 25 '18 at 12:22
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    $\begingroup$ Certainly, nested Ifs or a Which can help here... $\endgroup$ – Henrik Schumacher Apr 25 '18 at 12:44
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As Henrik Schumacher points out in a comment to the question, Which, which can be considered a multi-test version of If, can be used to solve your problem. Like so.

m = Table[Which[i == j, i, i < j, 1, True, 0], {i, 10}, {j, 10}];
m // MatrixForm

matrix

You could also use nested If expressions.

m = Table[If[i == j, i, If[i < j, 1, 0]], {i, 10}, {j, 10}];
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One using Switch and another using nested If:

m1 = Table[
   Switch[Positive[i - j], True, 0, False, 1; i], {i, 1, 10}, {j, 1, 
    10}];
m2 = Table[
   If[i - j == 0, i, If[i - j > 0, 0, 1]], {i, 1, 10}, {j, 1, 10}];
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