sqrt(complex(x)) error

The simulink circuit that I built has two different codes. but the error tells me that I need to put sqrt(complex(x)) which I do not use in my code. The only sqrt that I used are used in command form,%. It should not effect the program overall.

Below are the codes where I think the error comes from

function [THETA_1, THETA_2, THETA_3, THETA_4] = fcn(Px,Py,Pz)
%determine THETA_1
test = 2;
if test == 1
    Px = -0.02; Py = 0; Pz = 397.35;
elseif test ==2
    Px = -224.52; Py = 156.22; Pz = 387.34;
elseif test == 3
    Px = 63.37; Py = 14.74; Pz = 377.35;
elseif test == 4
    Px = 50.73; Py = 56.5; Pz = 367.35;
elseif test == 5
    Px = 247.56; Py = -93.02; Pz = 357.35;
elseif test == 6
    Px = 7.04; Py = -140.77;Pz = 347.36;
elseif test == 7
    Px = 24.77; Py = -25.69; Pz = 337.34;
elseif test == 8
    Px = -41.65; Py = 65.76; Pz = 327.36;
elseif test == 9
    Px = -60.48; Py = -49.01; Pz = 317.37;
elseif test == 10
    Px = -37.99; Py = -67.95; Pz = 307.35;
end

THETA_1 = atand(Py/Px);

%how to get c?
c = (Px^2 + (300 -(Pz+72)^2))^(1/2);

b=250; a=160;
THETA_C = acosd((a^2 + b^2 - c^2)/ 2*a*b);
%THETA_c = real (THETA_C);

THETA_3 = 180 - THETA_C;
THETA_A = asind(a/c)*(sind(THETA_C));
%THETA_a = real (THETA_A);

THETA_B = asind(b/c)*(sind(THETA_C));
%THETA_b = real (THETA_B);

THETA_E = atand(300/Px);
%THETA_e = real (THETA_E);

THETA_G = 90 -(THETA_E);THETA_D = THETA_G;

%h = sqrt(complex(300^2 + Px^2));
%h/sind(THETA_H) = c/sind(THETA_G) = (Pz+72)/sind(THETA_F)
%(Pz+72)/sind(THETA_F)= c/sind(THETA_G);
% c *sind(THETA_F) = (Pz+72)* sind(THETA_G)
%sind(THETA_F)= (sind(THETA_G)*(Pz+72))/c;
THETA_F = asind((sind(THETA_G)*(Pz+72))/c);
%THETA_f = real (THETA_F)

THETA_2 = 180 - THETA_A - THETA_D - THETA_F;  
THETA_H = 180 - THETA_G - THETA_F;
THETA_4 = 180 - THETA_B - THETA_H;

Below are the error that is shown in which I do not know where the error comes from. I really hope someone can point where my mistakes are. Thank you.

An error occurred while running the simulation and the simulation was terminated
Caused by:
Domain error. To compute complex results from real x, use 'sqrt(complex(x))'

[James Tursa]

The error is caused by having an argument to sqrt( ) that is negative. Or it can be caused by an argument to asin( ) or acos( ) that has magnitude greater than 1.

Answer 1

[Walter Roberson]

c = (Px^2 + (300 -(Pz+72)^2))^(1/2)

That is a square root.

You have 300 minus something that is squared. You want (300 minus something) squared if you want to be sure that you are are always taking the square root of a positive value.

[Syahirah Eshah]

I didn't notice that, thank you for pointing it out

[Lalitesh]

Hello, I am not expert in programming and I have faced the same issue. How to avoid this error ? could you please reply me in detail ?

[Walter Roberson]

c = (Px^2 + complex(300 -(Pz+72)^2))^(1/2)

would be the work-around for the case where you are deliberately allowing taking the square root of a negative value.