Error in the for loop or equality sign

Hello,

I am using following code to check the discharges in the pipelines connecting three reservoirs. But the Loop is not working I guess. Could anybody tell the error?

Ela=100;
Elb=70;
Elc=30;
ka=1563.085;
kb=38.10;
kc=12729.55;
x=70:0.01:75;
for i=1:x;
Qa=sqrt((Ela-x)/ka);
Qb=sqrt((x-Elb)/kb);
Qc=sqrt((x-Elc)/kc);
if Qb+Qc==Qa
 disp(Qa)
 disp(Qb)
 disp(Qc)
 break
else 
    continue
end
end

[Alex Mcaulley]

What do you mean by "is not working"? What do you expect?

[Walter Roberson]

x=70:0.01:75;
for i=1:x;

When you execute that for loop what do you expect the first value of i to be? What do you expect the second value of i to be? What do you expect the last value to be?

[Faisal Baig]

I want to check different values of Qa, Qb and Qc for given range of x until the sum Qb+Qc becomes equal to Qa. At that point, I want the code to show the values of Qa, Qb and Qc which satisfies the condition. But when I run the code, only I get the matrix of Qa, Qb, Qc agaisnt the given range of x and my condition (Qa=Qb+Qc) is not met somehow.

[Walter Roberson]

Please answer my question about the expected values of i

[Faisal Baig]

I can use

'for x= 70:0.01:75'

instead of

x= 70:0.01:75;

for i = 1:x;

So basically, I just want to give range of my values to find Qa, Qb and Qc. i doesn't matter

Answer 1

[Jos (10584)]

Welcome to the world of floating point arithmetic, where

if 0.1+0.2 == 0.3
    disp('0.1+0.2 equals 0.3')
else
    disp('0.1+0.2 does not equal 0.3')
end

More info here:

https://matlab.fandom.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

You want to check with a tolerance:

if abs(Qa+Qb-Qc) < 1e-10
    disp('Qa+Qb practically equals Qc')
end