I am trying to make my own function in matlab to solve for a system of two nonlinear equations, while using a nested function to share some some parameters, here is a sample code:
function y=solve(a,x0)
a;
y=fsolve(nle,x0); % this is line 3
function f=nle(x)
f(1)=x(1)-a*x(1)^2-x(1)*x(2); % this is line 6
f(2)=2*x(2)-x(2)+3*x(1)*x(2);
end
end
Here a is the parameter I want to pass from command line to the function, and x0 is the start point for the fsolve.
However, when I call the function in malab after specifying a=4 and x0=[1 1]', it gave me the following error:
Error using solve/nle (line 6)
Not enough input arguments.
Error in solve (line 3)
y=fsolve(nle,x0);
I'm quite a newbie for matlab, can anybody tell me where I am doing wrong?
Thanks in advance.
EDIT:
I tried substituting the nle with a function handle #nle, but seems something else went wrong:
Undefined function 'fsolve' for input arguments of type 'function_handle'.
Error in solve (line 3)
y=fsolve(#nle,x0);
Doesn't seem to make sense since I checked the documentation for fsolve, and it says it should indeed use a function handle there...
You miss the '#' in front of nle, i.e.
y = fsolve(#nle,x0);
should work.
Related
I'm trying to invoke an fgoalattain function (computing a function minimum with a goal-attainment algorithm) in MATLAB. According to documentation, it should look like this:
[X,FVAL,ATTAINFACTOR] = FGOALATTAIN(#objf_1,x0,goal,weight)
where #objf_1 is a function handle for a function defined in objf_1 m-file and the rest are some arguments I set on my own. They are not important in any case, because evidently MATLAB has a problem with that function, as it throws:
>> rospar_4
Undefined function 'fgoalattain' for input arguments of type 'function_handle'.
Error in rospar_4 (line 29)
[X,FVAL,ATTAINFACTOR] = fgoalattain(#objf_1,x0,goal,weight)
However, I already know that the function works fine on another MATLAB version - R2011b (the one I'm using is R2012b), but with first argument as char instead:
[X,FVAL,ATTAINFACTOR] = fgoalattain('objf_1',x0,goal,weight)
If I try to invoke it like this in mine though, the error is almost the same:
>> rospar_4
Undefined function 'fgoalattain' for input arguments of type 'char'.
Error in rospar_4 (line 29)
[X,FVAL,ATTAINFACTOR] = fgoalattain('objf_1',x0,goal,weight)
Any idea how am I getting this?
It is not a built-in function. You need to install the Optimization toolbox.
As part of a group project we have a system of 2 non linear differential equations and we have to draw the S=S(t) , I=I(t) graphic using the midpoint method.
And I'm getting the following error when trying to insert the matrix with the corresponding differential equations:
"Error in inline expression ==> matrix([[-(IS)/1000], [(IS)/1000 - (3*I)/10]])
Undefined function 'matrix' for input arguments of type 'double'.
Error in inline/subsref (line 23)
INLINE_OUT_ = inlineeval(INLINE_INPUTS_, INLINE_OBJ_.inputExpr, INLINE_OBJ_.expr);"
The code I have done is the following:
syms I S
u=[S;I];
F=[-0.001*S*I;0.001*S*I-0.3*I];
F1=inline(char(F),'I','S');
h=100; %Valores aleatórios
T=100000;
ni=(T/h);
u0=[799;1];
f=zeros(1,2);
k=zeros(1,2);
i=1;
while i<=ni
f(1)=F1(u0(1));
f(2)=F1(u0(2));
dx=h*f;
k(1)=F1((u0(1)+h*(1/2)),(u0(2)+h*(1/2)));
k(2)=F1((u0(1)+h*(1/2)),(u0(2)+h*(1/2)));
u1=u0+h*k;
disp('i:'),disp(i)
disp('u= '),disp(u1)
u0=u1;
i=i+1;
end
I'm new to this so the algorithm it's very likely to be wrong but if someone could help me with that error I'd apreciate it. Thank you!
The problem that specifically creates the error is that you are putting two symbolic functions into a matrix and then calling char (which outputs matrix([[-(IS)/1000], [(IS)/1000 - (3*I)/10]]) rather than converting nicely to string).
The secondary problem is that you are trying to pass two functions simultaneously to inline. inline creates a single function from a string (and using anonymous functions instead of inline is preferred anyway). You cannot put multiple functions in it.
You don't need sym here. In fact, avoid it (more trouble than it's worth) if you don't need to manipulate the equations at all. A common method is to create a cell array:
F{1} = #(I,S) -0.001*S*I;
F{2} = #(I,S) 0.001*S*I-0.3*I;
You can then pass in I and S as so:
F{1}(500,500)
Note that both your functions include both I and S, so they are always necessary. Reconsider what you were expecting when passing only one variable like this: f(1)=F1(u0(1));, because that will also give an error.
I am trying to minimize with respect to a variable "y" a function that contains a parameter which must be calculated as a solution of an equality that contains "y" as well (say, y=-3; in my complete problem it is an equation with no analytic closed form solution, so I really need fzero).
Because of this, I include the fzero function in the argument of fminsearch:
fminsearch( #(y) 10*fzero(#(y) y+3, 0)) ;
I get the error:
Error using fminsearch (line 85)
The input to FMINSEARCH should be either a structure with
valid fields or consist of at least two arguments.
I obviously get the same error with:
f = fzero(#(y) y+3, 0);
fminsearch(#(y) 10*f);
Apparently the problem is that I cannot "nest" a fzero inside fminsearch.
Any idea about how to turn around this problem?
If you read the error message you got and look at the documentation of fminsearch you'll see that you need to call it with two input arguments. You call it with only one.
fminsearch( #(y) 10*fzero(#(x) x+3, 0), 0 )
How do I easiest solve an equation=0 with a function as a parameter?
My function with one input variable is called potd(angle), with one output variable, potNRGderiv. I tried:
syms x
solve(potd(x))
This gave me error: Undefined function 'sind' for input arguments of type 'sym'.
Have you got any ideas? Thanks in advance.
solve is the wrong avenue here, unless your function can be rewritten as a simple equation. solve uses muPAD functions which is why you can do solve(sin(x)) but not solve(sind(x)). You can, of course, just do the conversion yourself.
If your function is more complicated or you'd rather not rewrite it, look into fsolve:
x = fsolve(#myfun,x0)
Where x0 is your initial guess - i.e. myfun(x0) is close to 0 - and myfun is a function which takes x and returns a single output. Depending on what your function does, you may have to adjust the options using optimoptions (tolerance, step size, etc) to get a good result.
I'm working on an assignment for a class of mine and I'm supposed to write a code using a program of my choice (I've chosen Matlab) to solve the Bessel function differential equation using the 4th order Runge-Kutta method. For reference the Bessel function DE is:
x^2*(J_n)''+x*(J_n)'+(x^2-n^2)*J_n=0.
I'm able to separate this into two coupled first order DEs by:
(J_n)'=Z_n and
(Z_n)'+(1/x)*Z_n+[(x^2-n^2)/x^2]*J_n=0.
I have no experience with Matlab nor any other programming language before this assignment. I know Matlab has the 'ode45' command but I'm supposed to write the code myself, not rely on Matlab's commands. So far I've been working on the n=0 case for the Bessel function but I keep getting an error when I try and plot the function. The current error I have says: "Undefined function or method 'J' for input arguments of type 'double'." But I don't know how to fix this error nor if my code is even correct. Could someone tell me where I've gone wrong or what is the correct way to write this code?
h=0.01; %step size
J_0(1)=1; %initial condition for J_0
Z_0(1)=1; %initial condition for Z_0-This value should be zero
%but Matlab gives me an error. To fix this, I input
%Z_0(1)-1 to use the correct value for Z_0(1).
x(1)=0.001; %first value of x
dZ(Z_0,J_0)=(-1/x)*(Z_0-1)-J_0;
for i=[1:1:10]
dZ1=(-1/x)*(Z_0-1)-J_0;
dJ1=(Z_0(1)-1)*h;
dZ2=(-1/x)*(Z_0-1+0.5*h)-(J_0+0.5*h*dJ1);
dJ2=((Z_0(1)-1)+dZ1)*h;
dZ3=(-1/x)*(Z_0-1+0.5*h)-(J_0+0.5*h*dJ2);
dJ3=((Z_0(1)-1)+dZ1+dZ2)*h;
dZ4=(-1/x)*(Z_0-1+h)-(J_0+h*dJ3);
dJ4=((Z_0(1)-1)+dZ1+dZ2+dZ3)*h;
J(i+1)=J(i)+(h/6)*(dJ1+2*dJ2+2*dJ3+dJ4);
end
plot(J_0);
Thanks in advance for any help
Your problem is on the line:
J(i+1)=J(i)+(h/6)*(dJ1+2*dJ2+2*dJ3+dJ4);
In the right-hand side of your assignment operator you use the variable J that is never set before i is taking the value 1. Looks like a typo to me (should it be J_0 instead?)
Also, don't forget your index i when computing your dJ and dZ stuff in the for loop.