Hi -- I've written a brief ado file to spit back characteristics of parametrized sinusoids (specifically, a 4-term Fourier series). The code is below. The mata code works fine when I run it on it's own --- say with a= .0005769, b= .0422043, c= .0131597, d= -.0168322 --- as an individual mata session. All four outputs (minimum, maximum, amplitude, lowpoint) are calculated, and all four also stored into a stata matrix that I can access after I end mata. However, when I call the ado as in the context at the bottom, it exports all matrices except lowpoint. I think I'm using minindex correctly --- it's underlined in red in the ado file whenever I store the index as anything but the letter i, but it does seem to work despite that --- and again, lowpoint *does* export to a stata matrix in individual mata sessions. Just now when run through the ado file. Any idea what's going on? Thank you!

** ADO FILE:
Code:
/* User written command by Leah E. M. Bevis */
/* December 2018 */
/* Input: coefficients (a,b,c,d) from the terms of this 4-term Fourier series: */
/* y = k + a*cos(2*pi*t/T1) + b*sin(2*pi*t/T1) + c*cos(2*pi*t/T2) + d*cos(2*pi*t/T2) */
/* Output: maximum, minimum, amplitude, index of lowest point */

program sinusoid
version 14.2
    args a b c d
    mata: FourierAmp(`a',`b',`c',`d')

end

version 14.2
mata: 
void FourierAmp(a, b, c, d) {

    t = (1::365)
    t=t/365
    
    T1=1
    omega1=2*pi()/T1
    T2=1/2
    omega2=2*pi()/T2

    y=a*cos(omega1*t) + b*sin(omega1*t) + c*cos(omega2*t) + d*sin(omega2*t)

    lowpoint=999
    w=999
    minindex(y,1,lowpoint,w) 
    
    minimum=min(y)
    maximum=max(y)
    amplitude=maximum-minimum

    st_matrix("minimum", minimum)
    st_matrix("maximum", maximum)
    st_matrix("amplitude", amplitude)
    st_matrix("lowpoint", lowpoint)

}
end

** CONTEXT FOR USE
Code:
reg Y csmnth snmnth csmnth2 snmnth2 
        local a = _b[csmnth]
        local b = _b[snmnth] 
        local c = _b[csmnth2]
        local d = _b[snmnth2] 
        sinusoid `a' `b' `c' `d'           
mat lis amplitude
mat lis minimum
mat lis maximum
mat lis lowpoint