Error using Cos, not enough input arguments

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Ned Sara 2019-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/454635-error-using-cos-not-enough-input-arguments

评论： Stephen23 2019-4-5

Hello, I'm having a problem with the cosine and sine functions in MatLab. I'm trying to replicate the effect of a plasma actuator in matlab which involves adding a source term that replicates the effect. The source term involve a Guassian function;

a = (cos^2*(pi/2)/2*Ox^2) + (sin^2*(pi/2)/2*Oy^2);

b = (-(sin*2*(pi/2)/4*Ox^2 + (sin*2*(pi/2)/4*Oy^2)));

c = (sin^2*(pi/2)/2*Ox^2) + (cos^2*(pi/2)/2*Oy^2);

with the source term being;

Su = A*exp(-(a(x-xc)^2 + 2*b(x-xc)*(y-yc) + x(y-yc)^2));

when i try running, it says error using cos, not enough input arguments. Does anyone know where im going wrong?

Thanks

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Answer 1

Stephen23 2019-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/454635-error-using-cos-not-enough-input-arguments#answer_369233

编辑：Stephen23 2019-4-5

在 MATLAB Online 中打开

cos^2*(pi/2) % incorrect
cos(pi/2)^2  % correct

Your code has several other syntax errors, such as:

Ox          % what does this mean?
Oy          % what does this mean?

and

b(...) % if this is supposed to be multiplication, then you actually need:
b*(...)

You should learn basic MATLAB concepts by doing the introdcutory tutorials:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

and also reading the documentation for every operation that you use, no matter how trivial you think it might be. You should also learn about vectorized code:

https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

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Ned Sara 2019-4-5

编辑：Stephen23 2019-4-5

在 MATLAB Online 中打开

Ox and Oy were reffering to sigma x and sigma y in the Guassian Function

clear; close all;
nx=101; ny=101; nt=500; nit=50;
 
xmin=-5; xmax=5;
ymin=0; ymax=8;
 
dx = (xmax-xmin)/(nx-1);
dy = (ymax-ymin)/(ny-1);
x = linspace(xmin,xmax,nx);
y = linspace(ymin,ymax,ny);
 
[X,Y] = meshgrid(x,y);
 
rho=1.225;
nu=0.000001;
dt=0.0000001;
 
source_posx = -2;
source_posy = 0;
source_h = 1;
source_w = 1.5;
 
A=0.5;
sigma_x = 0.5;
sigma_y = 0.5;
x = 2;
xc = 0.2;
y = 2;
yc = 0.2;
 
a = ((cos(pi/2)^2)/2*sigma_x^2) + ((sin(pi/2)^2)/2*sigma_y^2);
b = (-(sin*2*(pi/2)/4*sigma_x^2) + (sin*2*(pi/2)/4*sigma_y^2));
c = (sin(pi/2)^2)/(2*sigma_x^2) + (cos(pi/2)^2)/2*sigma_y^2;
 
% Source term
Su = A*exp(-(a*(x-xc)^2 + 2*b*(x-xc)*(y-yc) + c*(y-yc)^2));
Sv = 0.1;
 
 
% Init
u=zeros(ny,nx);
v=zeros(ny,nx);
p=zeros(ny,nx);
b=zeros(ny,nx);
%Pressure Field
%Square Brackets of Poissons Equation
 
 
for it = 1:nt+1
    
    for i=2:(nx-1)
        for j=2:(ny-1)
            b(i,j)=rho*(1/dt*((u(i+1,j)-u(i-1,j))/(2*dx)+(v(i,j+1)-v(i,j-1))/(2*dy))-((u(i+1,j)-u(i-1,j))/(2*dx))^2-2*((u(i,j+1)-u(i,j-1))/(2*dy)*(v(i+1,j)-v(i-1,j))/(2*dx))-((v(i,j+1)-v(i,j-1))/(2*dy))^2);
        end
    end
    
    for iit=1:nit+1
        pn=p;
        for i=2:(nx-1)
            for j=2:(ny-1)
                p(i,j)=((pn(i+1,j)+pn(i-1,j))*dy^2+(pn(i,j+1)+pn(i,j-1))*dx^2)/(2*(dx^2+dy^2))-dx^2*dy^2/(2*(dx^2+dy^2))*b(i,j);
            end
        end
        p(:,ny) = p(:,ny-1); %%dp/dy = 0 at y = 2
        p(1,:)  = p(2,:);    %%dp/dy = 0 at y = 0
        p(:,1)  = p(:,2);      %%dp/dx = 0 at x = 0
        p(:,ny) = 0;          %%dp = 0 at y = 2
        
    end
    
    un = u;
    vn = v;
    
    for j=2:nx-1
        for i=2:ny-1
            %Velocity Field
            
            % U components:
            u1 = un(i,j)*dt/dx*(un(i,j)-un(i-1,j));
            v1 = vn(i,j)*dt/dy*(un(i,j)-un(i,j-1));
            px = dt/(2*rho*dx)*(p(i+1,j)-p(i-1,j));
            ux = dt/dx^2*(un(i+1,j)-2*un(i,j)+un(i-1,j));
            uy = dt/dy^2*(un(i,j+1)-2*un(i,j)+un(i,j-1));
            
            % V components:
            u2 = un(i,j)*dt/dx*(vn(i,j)-vn(i-1,j));
            v2 = vn(i,j)*dt/dy*(vn(i,j)-vn(i,j-1));
            py = dt/(2*rho*dy)*(p(i,j+1)-p(i,j-1));
            vx = dt/dx^2*(vn(i+1,j)-2*vn(i,j)+vn(i-1,j));
            vy = dt/dy^2*(vn(i,j+1)-2*vn(i,j)+vn(i,j-1));
            
            inxrng = (X(i,j) >= source_posx-(0.5*source_w)) && (X(i,j) <= source_posx+(0.5*source_w));
            inyrng = (Y(i,j) >= source_posy-(0.5*source_h)) && (Y(i,j) <= source_posy+(0.5*source_h));
            
            u(i,j) = un(i,j)-u1-v1-px+nu*(ux + uy);
            v(i,j) = vn(i,j)-u2-v2-py+nu*(vx + vy);
            
            % Add source term
            if inxrng && inyrng
                u(i,j) = u(i,j) + Su;
                v(i,j) = v(i,j) + Sv;
            end
        end
        u(1,:)=0;
        u(:,1)=0;
        u(nx,:)=0;
        u(:,ny)=0;
        v(1,:)=0;
        v(ny,:)=0;
        v(:,1)=0;
        v(nx,:)=0;
        
    end
    %surf(x,y,u)
%     %contourf(x,y,sqrt(u.^2+v.^2),'linestyle','None')
%     quiver(x,y,u,v,5)
%     axis equal
%     pause(0.05)
    
    %surf(x,y,u)
    %pause(0.001)
end
 
quiver(x,y,u,v,5)
axis equal
pause(0.05)

That is the full code if it makes sense

Stephen23 2019-4-5

Learn how to write vectorized code.

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