Is it possible to simplify the expression using user-defined functions? For example if I define:
m[l_, x_] := Sum[x^i/i, {i, 1, l - 1}]
I would like
x + x^2/2 // FullSimplify
to returns
m[3, x]
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asked Feb 9 '19 at 23:34
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You can use the second argument of FullSimplify to specify (hopefully not too long) a list of equalities involving the forms that you wish to detect and keep in the input expression:
ClearAll[m]
m[l_, x_] := Sum[x^i / i, {i, 1, l-1}]
FullSimplify[10 + x + x^2/2, Array[m[#, x] == HoldForm[m[#, x]] &, 10]]
10 + m[3, x]
FullSimplify[5 + x + 5 (x + x^2/2) + y Log[x + x^2/2 + x^3/3],
Array[m[#, x] == HoldForm[m[#, x]] &, 10]]
5 + m[2, x]+ 5 m[3, x] + y Log[m[4, x]]
