How can i give multiple input values in this function?

2018 12 7
2 个回答
回答已采纳
更新时间：2018 12 7
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0 个投票

I have defined my function and I want to solve for P for multiple phi but it does not give me for different input values it soled for only one value.
I also tried to plot it but it does not give me any plot. Can anyone see my code and guide me it will be very helpfull for me. Thanks in advance.
Inuput values are (pi/6 , pi/3, pi/2, 2pi/3, 5pi/6, pi, 7pi/6, 4pi/3, 3pi/2, 5pi/3, 11pi/6).
function [P] = myfile(phi)
phi = [pi/6 pi/3 pi/2];
for i=1:length(phi)
A = 6*(0.8)*sin(phi);
B = 2+(0.8)*cos(phi);
C = 2+(0.8)^2;
D = (1+0.8*cos(phi)).^2;
P = (A.*B)/(C*D);
end
figure,plot(phi,P)
xlabel('Domain'),ylabel('Pressure'),
title('non-dimensional pressure'),
end

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 采纳的回答

Image Analyst
Image Analyst 2018-12-7

2 个投票

You did not include an index for P, so you just overwrite the same P every iteration. You should have done:
P(i) = (A.*B)/(C*D);
However, you can vectorize the code like this:
phi = [pi/6 , pi/3, pi/2, 2*pi/3, 5*pi/6, pi, 7*pi/6, 4*pi/3, 3*pi/2, 5*pi/3, 11*pi/6]
P = myfile(phi) % Call the myfile function
function P = myfile(phi)
A = 6*(0.8).*sin(phi);
B = 2+(0.8).*cos(phi);
C = 2+(0.8).^2 * ones(1, length(phi));
D = (1+0.8.*cos(phi)).^2;
P = (A.*B)./(C.*D);
figure
plot(phi,A, '*-', 'LineWidth', 2);
hold on;
plot(phi,B, '*-', 'LineWidth', 2);
plot(phi,C, '*-', 'LineWidth', 2);
plot(phi,D, '*-', 'LineWidth', 2);
plot(phi,P, '*-', 'LineWidth', 4);
xlabel('Domain');
ylabel('Pressure');
title('non-dimensional pressure');
legend('A', 'B', 'C', 'D', 'P');
grid on;
end
0001 Screenshot.png
I'm showing the individual A, B, C, and D, just for interest. You just have to change the definition of C slightly. Vectorization is something you should learn as it's one of the most powerful features of modern languages.

更多回答（1 个）

madhan ravi
madhan ravi 2018-12-7
编辑：madhan ravi 2018-12-7

1 个投票

EDITED
Loop can be avoided:
Phi=pi/6:pi/6:11*pi/6;
P = myfunc(phi); % function call
function P = myfunc(phi) % function definition
A = 6*(0.8).*sin(phi);
B = 2+(0.8).*cos(phi);
C = 2+(0.8).^2;
D = (1+0.8.*cos(phi)).^2;
P = (A.*B)./(C.*D);
figure,plot(phi,P)
xlabel('Domain'),ylabel('Pressure'),
title('non-dimensional pressure'),
end

6 个评论
显示 4更早的评论 隐藏 4更早的评论

Mirza Farrukh Baig
Mirza Farrukh Baig 2018-12-7
give me an error. Function with duplicate name "myfile" cannot be defiend.
madhan ravi
madhan ravi 2018-12-7
so you have some file named myfile change it's name or delete it
Mirza Farrukh Baig
Mirza Farrukh Baig 2018-12-7
Thanks for your help but i am not getting the P values in command window.
can I smothen the plot between the minumum and maximum values (range pi/6 to 11pi/6)? Can take more points between the?
madhan ravi
madhan ravi 2018-12-7
编辑：madhan ravi 2018-12-7
yes use interp1() using spline method to smoothen the curve or decrease the step size
FYI the below is the values I got(just copy and paste my edited answer and save it ina script and run it or save the function with the same name it has and just call it):
P =
Columns 1 through 3
0.854265687098479 1.92807139989114 3.63636363636364
Columns 4 through 6
6.99818508108637 12.5938246840688 3.09029394417163e-14
Columns 7 through 9
-12.5938246840688 -6.99818508108638 -3.63636363636364
Columns 10 through 11
-1.92807139989115 -0.85426568709848
Mirza Farrukh Baig
Mirza Farrukh Baig 2018-12-7
I used this but did not get the smooth plot.
phi = pi/6:pi/6:11*pi/6;
P = new(phi); % function call
eccentricity = 0.8;
function P = new(phi) % function definition
A = 6*(0.8).*sin(phi);
B = 2+(0.8).*cos(phi);
C = 2+(0.8).^2;
D = (1+0.8.*cos(phi)).^2;
P = (A.*B)./(C.*D);
figure
xq = 0:pi/6:2*pi;
w = interp1(phi,P,xq,'spline');
plot(xq,w)
xlabel('Domain'),ylabel('Pressure'),
title('non-dimensional pressure'),
end

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