how to plot 2 curve with together

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saman ahmadi
saman ahmadi 2020-8-5
评论： saman ahmadi 2020-8-5
Hi. i want to plot below the eqs. in matlab. i want to plot f and f1 with together in one graph and then g and g1 with together in another graph. thank you
m=0:0.01:50;
f= ((7*m - 7*(m.^2 - (226*m)/7 + 15009/49).^(1/2) + 127)/(7*(3*m + 1))).^(1/2);
f1= (2.^(1/2)*((3*m + 1)*(m + 1)).^(1/2))/(3*m + 1);
g=((7*m + 7*(m.^2 - (226*m)/7 + 15009/49).^(1/2) + 127)/(7*(3*m + 1))).^(1/2);
g1=-(2^(1/2)*((3*m + 1)*(m + 1)).^(1/2))/(3*m + 1);
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saman ahmadi
saman ahmadi 2020-8-5
I want to draw these equations as I said in the previous message. But I can not please help me. Thankful
Adam Danz
Adam Danz 2020-8-5
Why can't you?
Because of an error message?
Because you don't know what functions to use?
We can't help you if we don't understand what the problem is.

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回答（3 个）

Star Strider
Star Strider 2020-8-5
First, use element-wise multiplication and division:
m=0:0.01:50;
f= ((7*m - 7*(m.^2 - (226*m)/7 + 15009/49).^(1/2) + 127)./(7*(3*m + 1))).^(1/2);
f1= (2.^(1/2)*((3*m + 1).*(m + 1)).^(1/2))./(3*m + 1);
g=((7*m + 7*(m.^2 - (226*m)/7 + 15009/49).^(1/2) + 127)./(7*(3*m + 1))).^(1/2);
g1=-(2^(1/2)*((3*m + 1).*(m + 1)).^(1/2))./(3*m + 1);
Then to plot them:
figure
subplot(2,1,1)
plot(m, [f; f1])
legend('f','f1')
grid
subplot(2,1,2)
plot(m, [g; g1])
legend('g','g1')
grid
If you want them in separate figures:
figure
plot(m, [f; f1])
legend('f','f1')
grid
figure
plot(m, [g; g1])
legend('g','g1')
grid
.
Adam Danz
Adam Danz 2020-8-5
The code results in the error,
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the
first matrix matches the number of rows in the second matrix. To perform elementwise
multiplication, use '.*'.
However there are several other errors to address.
First error
The error is happening here in f1
(3*m + 1)*(m + 1)
because you're multiplying a [1x5001] vector by [1x5001] which disobeys matrix multiplication rules.
If you want to multiply those values piece-wise, you'll need to use ".*"
(3*m + 1).*(m + 1)
% ^
If you want to use matrix multiplication,
(3*m + 1).*(m + 1).'
% ^^
Second error
The same error is in g1. Now you know how to fix that.
Errors 3-5
Judging by you description, it seems that you expect the results to be vectors. The two corrections above will produce scalar values because the division marked below is matrix-division rather than element-wise division. Use "./" instead.
f= ((7*m - 7*(m.^2 - (226*m)/7 + 15009/49).^(1/2) + 127)./(7*(3*m + 1))).^(1/2);
% ^
The same is true for f1, g, and g1. Now you know how to fix that.
Rik
Rik 2020-8-5
doc hold
doc subplot
Or even the documentation of plot itself: direct link.

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