Is t a vector? If so, take a look at the first paragraph of the Description section of the documentation for the if keyword.
"if expression, statements, end evaluates an expression, and executes a group of statements when the expression is true. An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false."
If t is a vector, as I suspect, the body of the if will only be executed if ALL the elements of t are less than 1.5. If even one element of t is not less than 1.5, the body of the else will execute.
If you want your function to return a vector of values the same size as t whose values contain one of the two values LCREV_MAX or omega.*60.*gr/(2*pi), use logical indexing.
