Error using atan2 Inputs must be real.

this programme and function keep saying :

*Error using atan2 Inputs must be real. line 4 'function file'

*Error line 14 'main programme

i made 'px,py,pz' as coments cause i dont know its supose to help

ps :didn't with it either

Main programme :

clear
clc
clf
a2=6.5;a3=0;d3=1.9;d4=6;
% px=[-0.7;-2.52;-1.13;-4.60;1.00;1.68];
% py=[11.70;10.10;1.54;7.10;5.00;1.18];
% pz=[-0.90;-1.63;-6.93;-1.38;-3.00;-6.94];
t=0:23;
px=30*t'.*cos(t');
py=1200-(30*t'.^2)/(50*pi);
pz=30*t'.*sin(t');
[theta,t1,t2,t3,t4,t5,t6]=part2(a2,a3,d3,d4,px,py,pz);
pxx=cos(t1).*(sin(t2+t3)*d4+a3*cos(t2+t3)+a2*cos(t2))-d3*sin(t1);
pyy=sin(t1).*(sin(t2+t3).*cos(t5)+sin(t2+t3)*d4+a3*cos(t2+t3)+a2*cos(t2));
pzz=cos(t2+t3)*d4-a3*sin(t2+t3)-a2*sin(t2);
figure(1),plot(t,t6,'r')
hold on 
plot(t,t1,'k')
plot(t,t2,'b')
plot(t,t3,'m')
plot(t,t4,'g')
plot(t,t5,'c')
grid on
hod off
figure(2)
plot3(0.001*px,0.005*py,0.001*pz,'r',pxx,pyy,pzz,'b')
grid on
hold off 

The function file :

function [theta,t1,t2,t3,t4,t5,t6]=part2(a2,a3,d3,d4,px,py,pz)
t1=atan2(px(1),py(1))-atan2(d3,sqrt(px(1)^2+py(1)^2-d3^2));
k=(px(1)^2+py(1)^2+pz(1)^2-a2^2-a3^2-d3^2-d4^2)/2*a2;
t3=atan2(a3,d4)-atan2(k,sqrt(a3^2+d4^2-k(1)^2));
t23=antan2((-a3-a2*cos(t3))*pz(1)-(cos(t1)*px(1)+sin(t1)*py(1))*(d4-a2*sin(t3)),(a2*sin(t3)-d4)*pz(1)+(a3+a2*cos(t3))*(cos(t)*px(1)+sin(t1)*px(1)+sin(t1)*py(1)));
t2=t23-t3;t4=0;t5=0;t6=0;
c1=cos(t1);s1=sin(t1);c2=cos(t2);s2=sin(t2);c3=cos(t3);s3=sin(t3);c23=cos(t23);s23=sin(t23);c4=cos(t4);c5=cos(t5);s5=sin(t5);c6=cos(t6);s6=sin(t6);
r13=-c1*(c23*c4*s5+s23*c5)-s1*s4*s5;
r23=-s1*c(23*c4*s5+s23*c5)+c1*s4*s5;
r33=s23*c4*s5-c23*c5;
r11=c1*(c23*(c4*c5*c6-s4*s6)-s23*s5*c6)+s1*(s4*c5*c6+c4*s6);
r21=s1*(c23*(c4*c5*c6-s4*s6)-s23*s5*c6)-c1*(s4*c5*c6+c4*s6);
r31=-s23*(c4*c5*c6-s4*s6)-c23*s5*c6;
for i=2:24
t1(i,1)=atan2(px(i,1),py(i,1))-atan2(d3,sqrt(px(i,1)^2+py(i,1)^2-d3^2));
k(i,1)=(px(i,1)^2+p(i,1)^2+pz(i,1)^2-a2^2-a3^2-d3^2-d4^2)/2*a2;
t3(i,1)=atan2(a3,d4)-atan2(k(i,1),sqrt(a3^2+d4^2-k(i,1)^2));
t23(i,1)=atan2((-a3-a2*cos(t3(i-1,1)))*pz(i,1)-cos(t1(i-1,1))*px(i,1)+sin(t1(i-1,1))*py(i,1)*(d4-a2*sin(t3(i-1,1))),(a2*sin(t3(i-1,1))-d4)*pz(i,1)+(a3+a2*cos(t3(i-1,1)))*(cos(t1(i-1,1))*px(i,1)+sin(t1(i-1,1))*px(i,1)+sin(t1(i-1,1))*py(i,1)));

t2(i,1)=t23(i,1-t3(i,1));

c1=cos(t1(i-1,1));s1=sin(t1(i-1,1));c2=cos(t2(i-1,1));s2=sin(t2(i-1,1));c3=cos(t3(i-1,1));
s3=sin(t3(i-1,1));c23=cos(t23(i-1,1));s23=sin(t23(i-1,1));c4=cos(t4(i-1,1));s4=sin(t4(i-1,1));
c5=cos(t5(i-1,1));s5=sin(t5(i-1,1));c6=cos(t6(i-1,1));s6=cos(t6(i-1,1));
r13(i-1,1)=-c1*(c23*c4*s5+s23*c5)-s1*s4*s5;
r23(i-1,1)=-s1*(c23*c4*s5+s23*c5)+c1*s4*s5;
r33(i-1,1)=s23*c4*s5-c23*c5;

t4(i,1)=atan2(-r13(i-1,1)*s1+r23(i-1,1)*c1,-r13(i-1,1)*c1*c23-r23(i-1,1)*s1*c23+r33(i-1,1)*s23);

s5=-r13(i-1,1)*(c1*c23*c4+s1*s4)+r23(i-1,1)*(s1*c23*c4-c1*s4)-r33(i-1,1)*s23*c4;
c5=r11(i-1,1)*(-c3*s23)+r23(i-1,1)*(-s1*s23)+r33(i-1,1)*(-c23);
t5(i,1)=atan2(s5,c5);
r11(i-1,1)=c1*(c23*(c4*c5*c6-s4*s6)-s23*s5*c6)+s1*(s4*c5*c6+c4*s6);
s6=-r11(i-1,1)*(c1*c23*s4-s1*c4)-r21(i-1,1)*(s1*c23*s4+c1*c4)+r31(i-1,1)*s23*s4;
c6=r11(i-1,1)*((c1*c23*c4+s1*s4)*c5-c1*s23*s5)+r21(i-1,1)*((s1*c23*c4-c1*s4)*c5-c1*s23*s5)-r31(i-1,1)*(s23*c4*c5+c23*s5);
t6(i,1)=atan2(s6,c6);
end
theta=[t1,t2,t3,t4,t5,t6]

Answer 1

[Star Strider]

If you want to compute the phase angle of a complex number, use the angle function.

[abouda tebba]

It wasnt requested for But ill try it thank you

[Star Strider]

As always, my pleasure!

Answer 2

[Steven Lord]

Set an error breakpoint and run your code. When MATLAB stops on that line, look at the values you're passing into atan2 in the call on that line. My guess is that while you expect the value whose square root you're passing into atan2 to be either positive or zero it's actually very slightly negative due to floating point issues.

x = 0.3-0.2-0.1

x = -2.7756e-17

In exact arithmetic, x would be 0. But none of one-tenth, two-tenths, or three-tenths can be exactly represented in double precision so it's not. So sqrt(x) is complex not 0.

sqrt(x)

ans = 0.0000e+00 + 5.2684e-09i