Plot for different values

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Luccas S.
Luccas S. 2021-8-15
编辑： Luccas S. 2021-8-15
Hi, I'm trying to vary the value of Q but the values ​​aren't changing.
HfTOTAL = 26.8708
Hg = 30
Q = 0:50:450;
K = HfTOTAL./Q.^1.852
Hm = Hg + K.*Q.^1.852 % m
KQ = K.*Q.^1.852
plot(Q,Hm,'k','LineWidth',2)

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Walter Roberson
Walter Roberson 2021-8-15
Just for fun, let is assign Q.^1.852 to a variable, say Q18
HfTOTAL = 26.8708
Hg = 30
Q = 0:50:450;
Q18 = Q.^1.852;
K = HfTOTAL./Q18;
So K is something divided by Q18
Hm = Hg + K.*Q18 % m
And there you take K times Q18. But Q is something divided by Q18, so except for loss of precision due to round-off error, or inf or nan effects, then K*Q18 is going to be the same as the something that was then divided by Q18. So
Hm = Hg + repmat(HfTotal, 1, length(Q));
but that's just a repeated constant
KQ = K.*Q18
Again that is just the same as repmat(HfTotal, 1, length(Q)); so it is just a repeated constant.
plot(Q,Hm,'k','LineWidth',2)
You plot the different Q values with the repeated constant on the Y axes.
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Walter Roberson
Walter Roberson 2021-8-15
Ran in:
Using a for loop will not help.
HfTotal = 6
HfTotal = 6
for Q = 1 : 3
K(Q) = HfTotal./Q
end
K = 6
K = 1×2
6 3
K = 1×3
6 3 2
for Q = 1 : 3
Hm(Q) = K(Q) .* Q
end
Hm = 6
Hm = 1×2
6 6
Hm = 1×3
6 6 6
The problem is that you are multipling by the exact same thing you are dividing by.
Luccas S.
Luccas S. 2021-8-15
编辑：Luccas S. 2021-8-15
I found my mistake, silly thing.
I should be plotting as a function of the Q m³/h in a part I hadn't posted, and I was plotting as a function of the Q m³/s. Never that it was going to work.
Sometimes it's better to go for a walk and come back hahaha

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