[Maxima-discuss] find_root how to use it

[André F. <a.f...@gm...>]

A follow-up on my issue finding the full width at half height. I have tried
using the find_root instead so I define a function f(x)

/* [wxMaxima: input   start ] */
f(x) := -SplineSFitCrossCorr[1](x) - CrossCorrelationsShift[1]/2$
/* [wxMaxima: input   end   ] */

where -SplineSFitCrossCorr[1](x) is the spline I have made based on the
data and CrossCorrelationsShift[1]/2 is the half height of the peak I am
trying to find the width of. Then I run this

find_root(f(x),x,-15,15)

and I get this output (showing only part of it)

find_root([-(1.644898582136851*10^-4*x^3+0.007402043619615831*x^2+0.1081554815930787*x+0.4957946062003042)*
charfun(x<-14)-charfun(4<=x and x<5)*
(1.117076017317504*10^-4*x^3-0.001802508781380471*x^2+0.001147908066100174*x+0.040843879341963)-charfun(5<=x
and x<6)*
(1.073977735114262*10^-4*x^3-0.001737861358075608*x^2+8.24670949575862*10^-4*x+0.04138260786950352)-
charfun(3<=x and
x<4)*(1.052478698634486*10^-4*x^3-0.00172499199896085*x^2+8.378409364216931*10^-4*x+0.0412573021815343)-
charfun(6<=x and x<7)*
(9.379365045859012*10^-5*x^3-0.001492987143124559*x^2-6.445743401304309*10^-4*x+0.04432109844891611)-
charfun(2<=x and x<3)*
(8.728363099403584*10^-5*x^3-0.001563313849136134*x^2+.....,-
15.0,15.0)

Why isn't it evaluating it? Or am I using find_root wrong? There should be
two solutions f(x).