Why am I getting complex values?

In this portion of my code I am getting complex values for HJ. There are 3 loops and each loop has 4 pipes.

% pipe length in ft
ZL(1,1) = 10560; ZL(1,2) = 15840; ZL(1,3) = 10560; ZL(1,4) = 15840;
ZL(2,1) = 15840; ZL(2,2) = 13200; ZL(2,3) = 10560; ZL(2,4) = 10560;
ZL(3,1) = 15840; ZL(3,2) = 15840; ZL(3,3) = 15840; ZL(3,4) = 15840;
% pipe dimensions in feet
D(1,1) = 16/12; D(1,2) = 12/12; D(1,3) = 14/12; D(1,4) = 16/12;
D(2,1) = 16/12; D(2,2) = 14/12; D(2,3) = 12/12; D(2,4) = 16/12;
D(3,1) = 12/12; D(3,2) = 10/12; D(3,3) = 12/12; D(3,4) = 12/12;
%Initial Flow
Q(1,1) = 3.0; Q(1,2) = 1.5; Q(1,3) = -1.6; Q(1,4) = -4.0;
Q(2,1) = 3.8; Q(2,2) = 1.7; Q(2,3) = 0.3; Q(2,4) = -3.0;
Q(3,1) = 1.8; Q(3,2) = 0.4; Q(3,3) = -1.0; Q(3,4) = -1.5;
c= 140;
for i = 1:3
  for j = 1:4
    a = pi*D(i,j)^2 /4;
    HJ(i,j) = (3.022*((Q(i,j)/a)^1.85)*ZL(i,j))/(c^1.85*D(i,j)^1.165);
 end
end

[KSSV]

Attach code .m or copy it...not a pdf......

This time I have copied it for you...next time copy the code in the question.

[Anthony Cavalieri]

clc; clear;

% pipe length in ft

ZL(1,1) = 10560; ZL(1,2) = 15840; ZL(1,3) = 10560; ZL(1,4) = 15840;

ZL(2,1) = 15840; ZL(2,2) = 13200; ZL(2,3) = 10560; ZL(2,4) = 10560;

ZL(3,1) = 15840; ZL(3,2) = 15840; ZL(3,3) = 15840; ZL(3,4) = 15840;

% pipe dimensions in feet

D(1,1) = 16/12; D(1,2) = 12/12; D(1,3) = 14/12; D(1,4) = 16/12;

D(2,1) = 16/12; D(2,2) = 14/12; D(2,3) = 12/12; D(2,4) = 16/12;

D(3,1) = 12/12; D(3,2) = 10/12; D(3,3) = 12/12; D(3,4) = 12/12;

%Initial Flow

Q(1,1) = 3.0; Q(1,2) = 1.5; Q(1,3) = -1.6; Q(1,4) = -4.0;

Q(2,1) = 3.8; Q(2,2) = 1.7; Q(2,3) = 0.3; Q(2,4) = -3.0;

Q(3,1) = 1.8; Q(3,2) = 0.4; Q(3,3) = -1.0; Q(3,4) = -1.5;

c= 140;

for i = 1:3

for j = 1:4

a = pi*D(i,j)^2 /4;

HJ(i,j) = (3.022*((Q(i,j)/a)^1.85)*ZL(i,j))/(c^1.85*D(i,j)^1.165);

end

endclc; clear;

% pipe length in ft

ZL(1,1) = 10560; ZL(1,2) = 15840; ZL(1,3) = 10560; ZL(1,4) = 15840;

ZL(2,1) = 15840; ZL(2,2) = 13200; ZL(2,3) = 10560; ZL(2,4) = 10560;

ZL(3,1) = 15840; ZL(3,2) = 15840; ZL(3,3) = 15840; ZL(3,4) = 15840;

% pipe dimensions in feet

D(1,1) = 16/12; D(1,2) = 12/12; D(1,3) = 14/12; D(1,4) = 16/12;

D(2,1) = 16/12; D(2,2) = 14/12; D(2,3) = 12/12; D(2,4) = 16/12;

D(3,1) = 12/12; D(3,2) = 10/12; D(3,3) = 12/12; D(3,4) = 12/12;

%Initial Flow

Q(1,1) = 3.0; Q(1,2) = 1.5; Q(1,3) = -1.6; Q(1,4) = -4.0;

Q(2,1) = 3.8; Q(2,2) = 1.7; Q(2,3) = 0.3; Q(2,4) = -3.0;

Q(3,1) = 1.8; Q(3,2) = 0.4; Q(3,3) = -1.0; Q(3,4) = -1.5;

c= 140;

for i = 1:3

for j = 1:4

a = pi*D(i,j)^2 /4;

HJ(i,j) = (3.022*((Q(i,j)/a)^1.85)*ZL(i,j))/(c^1.85*D(i,j)^1.165);

end

end

[KSSV]

After quckly checking your pdf,,,see the matrix D, it has negative values.....the power of D i.e D^1.85 will be complex.

[KSSV]

You need not to define each elemtn of matrix...you can staright away type

D = [3  1.5 ....; ] 

Give all the elements in rows and columns..you can avoid typing more..be lazy. :)

Answer 1

[madhan ravi]

I don’t know why you’re surprised:

>> (-1)^1.85 % if the value is negative

ans =

     0.8910 - 0.4540i