Question: Problem during optimization

Hi everybody i've to minimize a function of about 5-6 variables so i tried some of maple functions like: 'Minimize', 'minimize', 'NLPSolve' but with 'minimize' my pc goes in loop and it eats a lot of ram without giving some results, while with the Optimization package i got the error :'

Error, (in Optimization:-NLPSolve) abs is not differentiable at non-real arguments

'

code :

restart;
L := 1:
b := 1.1:
p := 1.8:
xa := 0:
xd := -b/2:
ya := -p+z:
yd := 0:

quadrilatero := proc(q,xa,ya,xd,yd,l1,l2,l3,modo,alpha0,alpha1)
local xb,yb,l5,c,alpha,theta5,theta2,xc,yc,theta3,xm,ym:

xb := xa+l1*cos(q + alpha0 + pi/2):
yb := ya+l1*sin(q + alpha0 + pi/2):
l5 := sqrt((xd-xb)^2+(yd-yb)^2):
c := (l2^2+l5^2-l3^2)/(2*l2*l5):
if modo = 1 then alpha := arccos(c) else alpha := -arccos(c) end if:
theta5 := arctan(yd-yb,xd-xb):
theta2 := theta5 + alpha:
xc := xb + l2*cos(theta2 + pi):
yc := yb + l2*sin(theta2 + pi):
theta3 := arctan(yd-yc,xd-xc):
return (theta3 - pi - alpha1):
end proc:
#funione sterzo
f := proc(q,ya,l1,l2,l3,yd,alpha0,alpha1)
local theta;
theta := quadrilatero(q, 0, ya,-b/2,0, l1, l2, l3, -1,alpha0,alpha1) - pi/2;
if theta < Pi and Im(theta) = 0 then theta := theta + 2*pi end if;
return theta;
end proc:
#funzione desiderata
Yd(q) := arctan(tan(q),(1 - b*tan(q)/2/p));
arctan(tan(q), 1 - 0.3055555556 tan(q))

#Definisco procedura dei minimi quadrati:
n := 1: i := 0:
q := Vector[n]: rms := 0:
for i from 0 by 1 to (n-1) do
q[i] := Pi*(i/(4*n)):
rms := rms + abs(f(q[i],ya,l1,l2,l3,yd,alpha0,alpha1) - yd(q[i])^2):
end do:
rms := sqrt(rms / n):
#MIN := (minimize(rms, z = -0.4..0,alpha0 = 0..Pi/3,alpha1 = Pi/2..5*Pi/4,l1 = 0.3..1,l2 = 0.001..0.3,l3 = 0.01..0.3,iterationlimit = 100));
with(Optimization):
Optimization[NLPSolve](((rms)));
Error, (in Optimization:-NLPSolve) abs is not differentiable at non-real arguments

thanks in advance for your help !