not enough input arguments in function. Cannot get any output at all

function yp = equationb(t, y)

A=2.69; B=168; C=6270; D=59900; %coefficients
V = 10:50;

E= 15000000000; h = 0.048; I = (1/12)*h^4; l=4; rho=1600;
m = 0.177; c = 0.77; k = (48*E*I)/l^3; R = (0.5*rho*h);

yp (1) = y(2);
yp (2,1) = (R/m)*(A*V*y(2).^2 - (B*y(2).^4)/V + (C*y(2).^6)/V^3 - (D*y(2).^8)/V^5) - (c/m)*y(2) - (k/m)*y(1);

end

And my main function is

   close all; clear all; clc;

% Initial Conditions

h = 0.048;              %section width (m)
x0 = [h,10*h];          %initial displacements
v0 = zeros(length(x0)); %inital velocity
V = 10:50;              %flow velocity (m/s)

timespan = [0 30];

for j=1:length(x0)
      for k=1:length(V)
          a = [x0(1,j), v0(1,1), V(k)];

            [t,y] = ode15s(@equationb, timespan, a);      

          R = find(t>25); %returns a vector containing the linear indices of each nonzero element in array.
          LCO = y(R,1);
          maximum_amplitude(j,k) = max(LCO);  

      end
end

figure(1)
hold on; grid on; box on;
ylabel('Structural Displacement Amplitutde (m)')
xlabel('Air Flow Velocity (m/s)')
plot(V,maximum_amplitude(1,:),'go')
plot(V,maximum_amplitude(2,:),'r+')
axis([V(1) V(end) 0 0.7])

[Star Strider]

You need to re-write your ‘equationb’ ODE function. Pay special attention to the vector lengths and element-wise operations. I attempted to run it, but even after correcting the most obvious errors, could not figure out what you want to do with vector ‘V’.

[moonman1]

thank you. I corrected all the division and power errors. now i am getting the error "subscripted assignment dimension mismatch" ?

[Star Strider]

That is likely the problem with ‘V’ being a (1x5) vector and your ODE function being required to return a (2x1) vector, not a matrix. You have to figure out what you want to do with ‘V’.

[moonman1]

If I were to leave the ODE as it is, what would you suggest I do with V?

[Star Strider]

That depends on what ‘V’ is in your calculation. What are you doing with it?

[moonman1]

I am plotting it against " maximum_amplitude".

any tips?

Answer 1

[Star Strider]

This is one possible approach:

function yp = equationb(t, y, V)

Eliminate the vector definition of ‘V’ within ‘equationb’.

Change the call to ‘equationb’ to:

a = [x0(1,j), v0(1,1)];

[t,y] = ode15s(@(t,y)equationb(t,y,V(k)), timespan, a);

and see if that does what you want. (Having 3 initial conditions with a function that returns two derivatives will likely throw an error anyway. This should at least avoid that problem.)

[moonman1]

It got rid of that error, but now says I have too many input arguments.?

[Star Strider]

What line is throwing that error? The ode15s call I wrote should work.

It would help if you posted your revised code.

[moonman1]

It just says "Error using equationb Too many input arguments"

Here is my revised code:

 close all; clear all; clc;

h = 0.048;              %section width (m)
x0 = [h,10*h];          %initial displacements
v0 = zeros(length(x0)); %inital velocity
V = 10:50;              %flow velocity (m/s)

timespan = [0 30];

for j=1:length(x0) %cycle through the initial displacements
      for k=1:length(V) %cycle through all the flow velocities
          a = [x0(1,j), v0(1,1), V(k)]; %an array of the initial displacements, initial velocities and flow velocities

            %[t,y] = ode15s(@equationb, timespan, a);
            [t,y]=ode15s(@(t,y)equationb(t,y,V(k)),timespan, a);

            R = find(t>25); %returns a vector containing the linear indices of each nonzero element in array.
            LCO = y(R,1); %limit cycle oscillations
            maximum_amplitude(j,k) = max(LCO);  

        end
  end

figure(1)
hold on; grid on; box on;
ylabel('Structural Displacement Amplitutde (m)')
xlabel('Air Flow Velocity (m/s)')
plot(V,maximum_amplitude(1,:),'go')
plot(V,maximum_amplitude(2,:),'r+')
axis([V(1) V(end) 0 0.7])

    if true
      % code
    end
  *
  and the equation function:*

function yp = equationb(t,y)

A=2.69; B=168; C=6270; D=59900; %coefficients

E= 15000000000; h = 0.048; I = (1/12)*h^4; l=4; rho=1600;
m = 0.177; c = 0.77; k = (48*E*I)/l^3; R = (0.5*rho*h);

yp (1) = y(2);
yp (2,1) = (R/m)*(A*V*y(2).^2 - (B*y(2).^4)./V + (C*y(2).^6)./V.^3 - (D*y(2).^8)./V.^5) - (c/m)*y(2) - (k/m)*y(1);

end

[Star Strider]

You have to change the first line in your ‘equationb’ file as well:

function yp = equationb(t, y, V)

(I mentioned this in my original Answer.)

[moonman1]

apologies. I have that all fixed now.

here is the error i am receiving:

Error using odearguments (line 92) @(T,Y)EQUATIONB(T,Y,V(K)) returns a vector of length 2, but the length of initial conditions vector is 3. The vector returned by @(T,Y)EQUATIONB(T,Y,V(K)) and the initial conditions vector must have the same number of elements.

[Star Strider]

No worries.

I addressed that problem as well in my original Answer:

a = [x0(1,j), v0(1,1)];

[moonman1]

thank you based god.

you have solved the problem!

[Star Strider]

As always, my pleasure!