Wolframalpha replace part of equation with new variable

Question

How can I replace part of an equation in Wolframalpha with another variable? For instance if I have a matrix P = {{a+b+c+d+q/(p+a)-bc^2, a, b}, {q, a+b+c+d+q/(p+b)-bc^2, 0}, {1, 1, 1}}. How can I replace the a+b+c+d term with a new variable called s?

Answer 1

This answer is for Wolfram Mathematica, as tagged.

You can simply use ReplaceAll — shorthand /.

P = {
  {a + b + c + d + q/(p + a) - b c^2, a, b},
  {q, a + b + c + d + q/(p + b) - b c^2, 0},
  {1, 1, 1}}

newP =  P /. (a + b + c + d) -> s

{{-b c^2 + q/(a + p) + s, a, b}, {q, -b c^2 + q/(b + p) + s, 0}, {1, 1, 1}}

If you need to extract the pattern to be replaced from a more complex expression there are some tips here : How to group certain symbolic expressions?