How can i give multiple input values in this function?

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

Answer 1

[Image Analyst]

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

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.

[Mirza Farrukh Baig]

Thanks for your explanation.

Answer 2

[madhan ravi]

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

[Mirza Farrukh Baig]

give me an error. Function with duplicate name "myfile" cannot be defiend.

[madhan ravi]

so you have some file named myfile change it's name or delete it

[Mirza Farrukh Baig]

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]

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]

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

[madhan ravi]

xq = linspace(0,2*pi,1000);