Computes the relative error exponential.
input value
function value
var v = expm1rel( 0.0 ); // returns 1.0
var v = expm1rel( 1.0 ); // returns ~1.718
var v = expm1rel( -1.0 ); // returns ~0.632
var v = expm1rel( NaN ); // returns NaN
Computes the relative error exponential.