substituting multiple values in symbolic formula?

2018 6 29
1 个回答
回答已采纳
更新时间：2018 6 30
7 次查看（30 天）

0 个投票

I have this symbolic formula that is a variable of theta and phi, and I want to substitute the theta and phi with the following values in the following formula:
if true
% code
end
theta = -pi/2:pi/180:pi/2;
phi = -pi:pi/180:pi;
U = abs(sin(pi*cos(phi)*sin(theta))*sin(pi*sin(phi)*sin(theta)))^2/(abs(sin((pi*cos(phi)*sin(theta))/2))^2*abs(sin((pi*sin(phi)*sin(theta))/2))^2);

2 个评论
显示 无 隐藏 无

Ameer Hamza
Ameer Hamza 2018-6-30
theta and phi have different lengths. For substitution, they must have equal lengths.
Sharif Khalil
Sharif Khalil 2018-6-30
if they have equal length, how to do the substitution?

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Walter Roberson
Walter Roberson 2018-6-30

0 个投票

First create the symbolic formula. Next create your vectors of values but give them a different name than the variables in the formula. Then use ndgrid to create a grid of values for the two variables and use different variable names still. Finally,
Output = subs(U, {theta, phi}, {thetaGrid, phiGrid}) ;
There is another possibility that does not require creating the grid but it involves two subs calls and being careful about row and column vectors.

5 个评论
显示 3更早的评论 隐藏 3更早的评论

Sharif Khalil
Sharif Khalil 2018-6-30
编辑：Walter Roberson 2018-6-30
It also didn't work
syms theta phi real
Psi_x = k*dx*sin(theta)*cos(phi) + Beta_x;
Psi_y = k*dy*sin(theta)*sin(phi) + Beta_y;
AF_Field = (sin(Nx*Psi_x/2)/(sin(Psi_x/2)))*...
(sin(Ny*Psi_y/2)/(sin(Psi_y/2)));
U = abs((fi*AF_Field)).^2;
Theta = -pi/2:pi/180:pi/2; % Elevation Angle (radian)
Phi = -pi:pi/180:pi; % Azimuth Angle (radian)
Urad = subs(U, {theta, phi}, {Theta, Phi}) ;
Walter Roberson
Walter Roberson 2018-6-30
I do not see any call to ndgrid?
Sharif Khalil
Sharif Khalil 2018-6-30
could you please tell me how to do it
Walter Roberson
Walter Roberson 2018-6-30
编辑：Walter Roberson 2018-6-30
1) First create the symbolic formula.
syms theta phi real
Psi_x = k*dx*sin(theta)*cos(phi) + Beta_x;
Psi_y = k*dy*sin(theta)*sin(phi) + Beta_y;
AF_Field = (sin(Nx*Psi_x/2)/(sin(Psi_x/2)))*...
(sin(Ny*Psi_y/2)/(sin(Psi_y/2)));
U = abs((fi*AF_Field)).^2;
2) Next create your vectors of values but give them a different name than the variables in the formula.
Theta = -pi/2:pi/180:pi/2; % Elevation Angle (radian)
Phi = -pi:pi/180:pi; % Azimuth Angle (radian)
3) Then use ndgrid to create a grid of values for the two variables and use different variable names still.
[thetaGrid, phiGrid] = ndgrid(Theta, Phi);
4) Finally,
Output = subs(U, {theta, phi}, {thetaGrid, phiGrid}) ;

请先登录，再进行评论。

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Calculus 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by