Plot for different values

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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)

Accepted Answer

Walter Roberson
Walter Roberson on 15 Aug 2021
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.
  5 Comments
luccas santos
luccas santos on 15 Aug 2021
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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