# Simplifying Algebraic Expression With Substitution

Is there a way I can make an algebraic substitution in a matrix? I tried using

Simplify[P_rhs _ 51, (c44hat*rhohat)^.5 == zeta]


Where P_rhs_51 is a 4x4 matrix.

2 x 2 example:

P51 = {{(rhohat*c44hat)^.5, -(rhohat*c44hat)^.5}, {rhohat, rhohat}};

• You must not use underscores (_) for variable names in Mathematica. They have a built-in meaning (see Blank). You might also be interested in ReplaceAll (and its infix form /.). Feb 19 '19 at 10:58
• Yes, there is such a way. You may get a better answer, if you post your expressions, such that we could copy/paste and play with them. Feb 19 '19 at 11:01
• P51 = {{(rhohatc44hat)^.5, -(rhohatc44hat)^.5}, {rhohat, rhohat}} Feb 19 '19 at 11:05

P51 = {{(rhohat*c44hat)^.5, -(rhohat*c44hat)^.5}, {rhohat, rhohat}};