expr2=coll​ect(EXPR,'​exp(-t)') Why is it wrong?

EXPR=str2sym('(x^2+x*exp(-t)+1)*(x+exp(-t))')

expr1=collect(EXPR)

expr2=collect(EXPR,'exp(-t)')

Why expr2 shows: sym.charToFunction (line 26) Invalid variable name

Answer 1

[madhan ravi]

expr2=collect(EXPR,exp(-t)) % no single quotes around the second argument