Unevaluated form of an expresion

Question

I have two matrices - s1 and s2.

I want their sum to remain unevaluated.

For instance, the command

s1 + s2 // MatrixForm

should result to two separate matrices joined by the plus operator.

I guess that I have to wrap s1 + s2 inside a function like Hold or Unevaluated, but I cannot find the proper workaround.

Any ideas?

Sektor, thanks for the required modifications. I totally forgot them:-)! — Dimitris, May 07 '15 at 11:41
Hi, ilian and thank you. Is there any alternative for versions prior to 10? — Dimitris, May 07 '15 at 11:45
If just for display purposes, maybe Row[{MatrixForm[s1] , "+", MatrixForm[s2]}] ? — ilian, May 07 '15 at 11:48
As a matter of fact, I cannot understand why command Defer[s1+s2] returns s1+s2. — Dimitris, May 07 '15 at 11:54
@Kuba I think this might be considered a duplicate of that one; what do you think? — Mr.Wizard, May 07 '15 at 12:59
@Mr.Wizard I think so, but since there is V10 the linked topic needs merges/linkes or new answers with showcases of Inactive too. — Kuba, May 07 '15 at 13:02
@Kuba Okay, why don't you answer 31727 with Inactive and I shall close this one as a duplicate of it? — Mr.Wizard, May 07 '15 at 13:03
Try this ReplacePart[ ReplacePart[ HoldForm[s1 + s2], {1, 1} -> (s1 // MatrixForm)], {1, 2} -> (s2 // MatrixForm)] — Alexei Boulbitch, May 07 '15 at 13:15
@Mr.Wizard Do this now and I will try to find closely related topic later. I think I saw them but don't have time now. — Kuba, May 07 '15 at 13:16

xyz · Accepted Answer · 2015-05-08T05:08:25.703

s1 = {{8, 6, 6, 1}, {9, 8, 4, 4}, {5, 3, 5, 5}, {10, 5, 6, 2}};
s2 = {{9, 1, 10, 5}, {1, 9, 1, 3}, {8, 4, 4, 9}, {2, 9, 6, 2}};
Apply[
 HoldForm[#1 + #2] &, 
 MapThread[List, {s1, s2}, 2], {2}] // MatrixForm

$\left( \begin{array}{cccc} 8+9 & 6+1 & 6+10 & 1+5 \\ 9+1 & 8+9 & 4+1 & 4+3 \\ 5+8 & 3+4 & 5+4 & 5+9 \\ 10+2 & 5+9 & 6+6 & 2+2 \\ \end{array} \right)$

Or

SetAttributes[plus, Listable]
Apply[
 HoldForm[#1 + #2] &, plus[s1, s2], {2}] // MatrixForm

(same result)

Unevaluated form of an expresion

1 Answers1