Problem with function definition for mm_root

[Craig Landry]

I'm attempting to find the root of a non-linear equation using mata. Running Stata 15.1 on MacOS Mojave 10.14.6. Here is my code:

mata
maxu = 2.63506
u3 = 836.8054
u4 = 117.3982
u2 = 4.283902
w = 60.069
function myfunc(x, maxu, u3, u4, u2, w) return(maxu - ln(u3+u4+u2*exp(.0175134(w-x))))

rc = mm_root(x=., &myfunc(), 0, 1, 0 , 1000, maxu, u3, u4, u2, w)
x
end

This is the error message I'm getting:

: function myfunc(x, maxu, u3, u4, u2, w) return(maxu - ln(u3+u4+u2*exp(.0175134(w-x))))
invalid expression
r(3000);

Any suggestions? Thanks.

[William Lisowski]

You are missing an operator in your returned expression. Perhaps

function myfunc(x, maxu, u3, u4, u2, w) return(maxu - ln(u3+u4+u2*exp(.0175134*(w-x))))

is what you intended.

[Craig Landry]

Whoops. So simple. Thank you very much.

[Craig Landry]

I have it working, but mm_root is returning a missing value for the root (despite the fact that rc==0):

mata
maxu = 2.63506
u3 = 836.8054
u4 = 117.3982
u2 = 4.283902
w = 60.069
function wtp(x, maxu, u3, u4, u2, w) return(maxu - ln(u3+u4+u2*exp(.0175134*(w+x))))

rc = mm_root(x=., &wtp(), 0, 1000000, 0 , 10000, maxu, u3, u4, u2, w)
rc
x
end

[Craig Landry]

Found another error. Root-finding is running great now.