enter image description here

how can i get the following figure using the for loop.


The code I found is above but not working.where is the mistake?


1 Answer 1


Welcome to MMA SE! What the code above does is simply repeatedly overwrite the value of A. In each iteration of the loop, it evaluates A = i + j, so the A at the end of the loop is simply i + j for the last i, j in the loop.

You could do a For loop where you initialize A to a table, and then set different parts of A, e.g. A[[i,j]] = "*". That's not advisable in Mathematica, but it would look like this:

A = ConstantArray["", {n,n}];
For[i=1,i<=n,i++,For[j=1,j<=i,j++,A[[i,j]] = "*"]];
A // Grid

(Note an important change from the given code: we use j <= i, not j <= n.)

But it's far easier to simply use Table (or Array, for an alternative approach) to generate matrices, with a conditional statement in each entry that test if i < j:

Table[If[i < j, "", "*"], {i, 6}, {j, 6}] // Grid

Another way: you could also use LowerTriangularize on a 6 by 6 ConstantArray of "*", and replace all the resulting 0s in the upper triangle with "":

(LowerTriangularize[ConstantArray["*", {6, 6}]] /. (0 -> "")) // Grid
  • $\begingroup$ i understand you very well. i am much obligated. thank you very much $\endgroup$
    – hazal
    Apr 6, 2021 at 23:45
  • $\begingroup$ @hazal no problem, glad I could help, and of course feel free to let me know if you have any questions! $\endgroup$
    – thorimur
    Apr 6, 2021 at 23:57

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