# Question:eval and subexpressions

## Question:eval and subexpressions

Maple 2019

The command eval allows to simplify a complicated expression

in a more compact form for a later output in LATEX

In the example which follows I was able to insert A and B but non C in the expression.

There is already a post on this kind of topic but I failed to understand the details.

Perhaps a Maple worksheet of answer on this topic  would be useful !

bye Lorenzo

 > restart;
 > expression:=exp(-b*x^c/2)*((x^(-(3*c)/2 + a/2 + 1/2)*(c + a + 1)*b^(-(3*c + a + 1)/(2*c)) + c*x^(a/2 + 1/2 - c/2)*b^(-(c + a + 1)/(2*c)))*c*WhittakerM((-c + a + 1)/(2*c), (2*c + a + 1)/(2*c), b*x^c) + b^(-(3*c + a + 1)/(2*c))*x^(-(3*c)/2 + a/2 + 1/2)*WhittakerM((c + a + 1)/(2*c), (2*c + a + 1)/(2*c), b*x^c)*(c + a + 1)^2)/((a + 1)*(c + a + 1)*(2*c + a + 1));
 (1)
 (2)
 > expression_ABC:=eval(expression,[x^(-(3*c)/2 + a/2 + 1/2)*(c + a + 1)*b^(-(3*c + a + 1)/(2*c))=A,c*x^(a/2 + 1/2 - c/2)*b^(-(c + a + 1)/(2*c))=B,((a + 1)*(c + a + 1)*(2*c + a + 1))=C]);
 (3)
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