I'm evaluating a series of theoretical (not necessarily functional) circuits in matlab. I have been trying to get the transfer function of the circuits and during the process I use the sym2poly function. Sometimes, sym2poly works and returns the transfer function. Sometimes it does not.
This is what the code looks like:
[n,d] = numden(eval(v_3/V));
transH = tf(sym2poly(n),sym2poly(d))
n and d are symbolic cell arrays. The error I get is:
Error using sym/sym2poly (line 28)
Not a polynomial.
Error in CircuitGA (line 349)
n = sym2poly(n);
This looks similar to several questions posted a long time ago, but all of those were solved by a bug fix in an updated version of the symbolic math toolbox. Does it mean that what I am giving it is impossible to turn into a polynomial?
Is there a fix?
Any suggestions of a method that will work for all my circuit arrays?
Maybe a try and catch for if it can return a transfer function?
Related
This question already exists:
Error using symengine>#()0.0 Too many input arguments
Closed 3 years ago.
Exact error is:
Error using symengine>#()0.0
Too many input arguments.
Error in bdipuniodefun (line 18)
bdip = [s(4); s(5); s(6); (q/m_e)*(Ex(s(1),s(2),s(3)) + s(5)*Bz(s(1),s(2),s(3)) - s(6)*By(s(1),s(2),s(3))); (q/m_e)*(Ey(s(1),s(2),s(3)) +
s(6)*Bx(s(1),s(2),s(3)) - s(4)*Bz(s(1),s(2),s(3))); (q/m_e)*(Ez(s(1),s(2),s(3)) + s(4)*By(s(1),s(2),s(3)) - s(5)*Bx(s(1),s(2),s(3)))];
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode15s (line 150)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in collisions6 (line 219)
[T,S] = ode15s(#bdipuniodefun, tspan, icv);
So we know where the error occurs, but I have been unable to resolve it nonetheless. This is an error that has also been inconsistent too. It does not always appear when I run the main script "collisions.m" but happens only when certain things get altered. Some examples: I start with too many electrons/particles, usually 1000+. Or I try to input a non-zero electric field. The electric field function is still being referenced but it is zero (Here comes the strange part). The reason I did this is because although the error goes away, the ode solver does not compute even close to the correct solutions I am looking for. I know for a fact that the results are wrong due to my knowledge of physics. However, when it does this, it does not give an error.
A Matlab staff member suggested that it may have something to due with my persistent variable definition but that is the only possible lead I have.
Troubleshooting methods I have already been through:
First if you look at the documentation from Matlab, it shows a specific syntax example to define the set of ODEs. In Matlab's syntax, they define each equation individually and then the vector of equations using the definitions. When I tried this syntax, the solver either did not solve the equations correctly, or it gave me the "too many input arguments" error. The way I made it run at all was to define every equation outright on a single line in "bdipodefun.m". Only that syntax worked and there is no good reason in my mind why this is the case because the definition that is used in one of the input arguments for the solver is the same. Using the Matlab recommended syntax even in simpler code, makes the ode solution incorrect.
I tried all ode solvers Matlab has to offer. The same issues persist or it cannot solve the equations at all.
I tried re-coding the entire simulation from scratch. I have found that this error still occurs even in more simpler codes.
Equation solver will also not solve the system correctly if there is no E-field. I found that if I create an E-field function and even just define it as zero within the file, the system solves correctly. It absolutely makes no sense as to why this is occurring.
Here is a description of what each file does in the code:
"collisionsmain.m" = Main script that references other files
"B_test.m" = B field function file referenced by collisionsmain
"E_test.m" = E field function file referenced by collisionsmain
"engen.m" = Generates energies for electrons based on a Maxwellian probability distribution curve
"maxdis.m" = Maxwellian distribution function used by engen
"engen.m" = Generates energies for electrons based on a Maxwellian
"posgen.m" = Generates a random, initial position on a sphere "bdipodefun.m" = ODE function set referenced by ODE solver in collisionsmain
Link to files: https://drive.google.com/drive/folders/19eJrgWYL4LQFwTY-VwguCCkta-pimZlL?usp=sharing
I didn't understand the code because it is complicated and big. Anyway, I tracked the error and find the source of the issue. The error comes from the number of parameters that have been sent to Ex, Ey, Ez in bdipuniodefun.m function. Ex, Ey, Ez functions receives 3 parameters while they can handle one parameter only.
The following code didn't send error and it shows the results.
bdip_r1 = [s(4); s(5); s(6)];
bdip_r2 = (q/m_e) * (Ex(s(1)) + s(5)*Bz(s(1),s(2),s(3))- s(6)*By(s(1),s(2),s(3)));
bdip_r3 = (q/m_e)*(Ey(s(1)) + s(6)*Bx(s(1),s(2),s(3)) - s(4)*Bz(s(1),s(2),s(3)));
bdip_r4 = (q/m_e)*(Ez(s(1)) + s(4)*By(s(1),s(2),s(3)) - s(5)*Bx(s(1),s(2),s(3)));
bdip =[bdip_r1;bdip_r2;bdip_r3;bdip_r4];
I am using MATLAB R2015 and cannot implement 'butter' without getting an error related to too many output arguments from the polyfit part of the script. I have used the same implementation for years with other versions of MATLAB.
Example:
[b, a] = butter(2,[.15,.3]);
Error using poly
Too many output arguments.
Error in zp2ss (line 127)
den = real(poly(p(i:i+1)));
Error in butter (line 97)
[a,b,c,d] = zp2ss(z,p,k);
I get the same error implementing the examples in the help documentation.
Just a guess but is there any chance you've defined your own poly function? which('poly') should point to some Matlab directory unless you've defined it elsewhere, potentially as a variable?. For me on a newer version that path is something like $MATLAB/toolbox/matlab/polyfun/poly.m You can also edit the poly function edit poly and verify that there is one output argument for the function.
Also, I'd advise against ever writing decimal numbers without a leading zero. It took me way to long to figure out what [.15,.3] was. Instead write [0.15,0.3] or even just [0.15 0.3] Edit: I just realized that is an example in Matlab ... my point stands but the toolbox author should know better ...
I am trying to run code similar to the following, I replaced the function I had with one much smaller, to provide a minimum working example:
clear
syms k m
n=2;
symsum(symsum(k*m,m,0,min(k,n-k)),k,0,n)
I receive the following error message:
"Error using sym/min (line 86)
Input arguments must be convertible to floating-point numbers."
I think this means that the min function cannot be used with symbolic arguments. However, I was hoping that MATLAB would be substituting in actual numbers through its iterations of k=0:n.
Is there a way to get this to work? Any help much appreciated. So far I the most relevant page I found was here, but I am somewhat hesitant as I find it difficult to understand what this function does.
EDIT following #horchler, I messed around putting it in various places to try and make it work, and this one did:
clear
syms k m
n=2;
symsum(symsum(k*m,m,0,feval(symengine, 'min', k,n-k)),k,0,n)
Because I do not really understand this feval function, I was curious to whether there was a better, perhaps more commonly-used solution. Although it is a different function, there are many pieces online advising against the eval function, for example. I thought perhaps this one may also carry issues.
I agree that Matlab should be able to solve this as you expect, even though the documentation is clear that it won't.
Why the issue occurs
The problem is due the inner symbolic summation, and the min function itself, being evaluated first:
symsum(k*m,m,0,min(k,n-k))
In this case, the input arguments to sym/min are not "convertible to floating-point numbers" as k is a symbolic variable. It is only after you wrap the above in another symbolic summation that k becomes clearly defined and could conceivably be reduced to numbers, but the inner expression has already generated an error so it's too late.
I think that it's a poor choice for sym/min to return an error. Rather, it should just return itself. This is what the sym/int function does when it can't evaluate an integral symbolically or numerically. MuPAD (see below) and Mathematica 10 also do something like this as well for their min functions.
About the workaround
This directly calls a MuPAD's min function. Calling MuPAD functions from Matlab is discussed in more detail in this article from The MathWorks.
If you like, you can wrap it in a function or an anonymous function to make calling it cleaner, e.g.:
symmin = #(x,y)feval(symengine,'min',x,y);
Then, you code would simply be:
syms k m
n = 2;
symsum(symsum(k*m,m,0,symmin(k,n-k)),k,0,n)
If you look at the code for sym/min in the Symbolic Math toolbox (type edit sym/min in your Command Window), you'll see that it's based on a different function: symobj::maxmin. I don't know why it doesn't just call MuPAD's min, other than performance reasons perhaps. You might consider filing a service request with The MathWorks to ask about this issue.
I've just updated to Matlab 2014a finally. I have loads of scripts that use the Symbolic Math Toolbox that used to work fine, but now hit the following error:
Error using mupadmex
Error in MuPAD command: Division by zero. [_power]
Evaluating: symobj::trysubs
I can't post my actual code here, but here is a simplified example:
syms f x y
f = x/y
results = double(subs(f, {'x','y'}, {1:10,-4:5}))
In my actual script I'm passing two 23x23 grids of values to a complicated function and I don't know in advance which of these values will result in the divide by zero. Everything I can find on Google just tells me not to attempt an evaluation that will result in the divide by zero. Not helpful! I used to get 'inf' (or 'NaN' - I can't specifically remember) for those it could not evaluate that I could easily filter for when I do the next steps on this data.
Does anyone know how to force Matlab 2014a back to that behaviour rather than throwing the error? Or am I doomed to running an older version of Matlab forever or going through the significant pain of changing my approach to this to avoid the divide by zero?
You could define a division which has the behaviour you want, this division function returns inf for division by zero:
mydiv=#(x,y)x/(dirac(y)+y)+dirac(y)
f = mydiv(x,y)
results = double(subs(f, {'x','y'}, {1:10,-4:5}))
When trying to compute this sequence I get an error
syms n
limit(((-3)^n)/factorial(n),inf)
Error using factorial (line 17)
N must be a matrix of non-negative integers.
Error in (line 9)
How do you fix this or specify the matrix they want?
The factorial function wasn't designed for use of symbolic references, and often chokes on them. It might work if you have a new enough version (2012b claims it works), but I don't think it'll necessarily work with older versions, I've found some documents claiming it won't in fact. The following two methods have been suggested to work around the problem.
limit((-3)^n/sym('n!'),n,inf)
limit((-3)^n/gamma(n+1),n,inf)