Amazing about lolremez

[samhocevar]

The range is indeed the problem. It states what the valid range for the resulting polynomial is (it is impossible to create an approximation polynomial for arbitrarily large values). So if you want to be able to compute exp(5) you will need to provide a larger range, e.g.:

lolremez -d 10 -r -5:5 "exp(x)" "exp(x)"

This will give the following value:

148.303891984497

That’s already closer. Another problem is that exp(x) behaves very differently for positive and negative values, so I suggest only computing for the 0:5 range:

lolremez -d 10 -r -0:5 "exp(x)" "exp(x)"

And calling the function like this:

x >= 0 ? exp(x) : 1.0 / exp(x)

This is the value for exp(5):

148.413082305473

Also note that if you use exp(x) as the error function, exp(5) will be the less precise value. You may wish to distribute the error in a more homogeneous way:

lolremez -d 10 -r -0:5 "exp(x)"

Which gives for exp(5):

148.413150926903