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Stefan Wehmeier

MathWorks

Active since 2011

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Working on the symbolic toolbox, mostly in the MuPAD language. Responsible for solvers and simplifiers.
Professional Interests: computer algebra

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Answered
How to stop MATLAB livescript from simplifying the answer?
Use sympref('AbbreviateOutput', false)

7 years ago | 3

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Answered
These equations have an answer - how to get solve to find it?
Why not just solve(expression1 == expression2, u) ? What you did is to confuse assignemnts/assumptions with equations. You ...

7 years ago | 0

Answered
Function Iteration for n times, but n is NOT a fixed number
Why don't you make your last source code the body of a function? Is l at any time called with non-constant argument, such that y...

7 years ago | 0

Answered
an error in new versions? triognometric function of A*t
It is a matter of taste if you prefer results in terms of exp or sin. You could do simplify(rewrite(A1, 'sin'))

7 years ago | 1

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Answered
Symbolic toolbox mpower unexpected behaviour
You can use symbolic N but not in connection with mpower. As T^N = exp(N*log(T)), write TN = expm(N*logm(T)) and procee...

7 years ago | 1

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Answered
mupad command calling from matlab produce wrong results
I cannot reproduce this. In any case, you cannot work with intervals in MATLAB; this is why poles(f) gives you just the ...

7 years ago | 0

Answered
Why does eig(A) not return a symbolic array for my symbolic matrix A?
The roots of polynomials of degree > 4 usually do not have a symbolic representation. The same holds for eigenvalues as they are...

9 years ago | 0

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Answered
Simplify expression with exponential function.
Use exp(sym(1))

9 years ago | 2

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Answered
Parametric solutions to system of equations inequations via solve()
I see that you are using R2014a. Then your only option is to solve for one variable solve(e(1) == 0, a) and take this as...

10 years ago | 0

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Answered
subs(a,b,1) introduces variable b into a?
I cannot reproduce this. If it happens (in which version ??), then it is clearly unexpected.

10 years ago | 0

Answered
Problems with matlab symbolic dsolve function
The correct syntax is syms y(x) dsolve(diff(y, x, x) +y==x*exp(-x^2)) as it declares y as a function of x (and not of...

10 years ago | 0

Answered
Matlab 2012b too slow when solving a system of two equations on mupadmex(statement)
A running time of one hour can be normal if the equations are very complicated. Since your code does not run as it stands, it is...

10 years ago | 0

Answered
Symbolic array pre-allocation
My question is in which form do you have the 50000 entries you want to fill in. As strings in a cell array A? Then B = cell...

10 years ago | 0

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Answered
Find conditions such that symbolic expression is real-valued
a) feval(symengine, 'solve', a*x^2 + b*x + c, x, 'Real', 'IgnoreSpecialCases') You may omit the IgnoreSpecialCases, whic...

12 years ago | 0

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Answered
simplifying symbolic expression in terms of other variables
You could also try syms a b x assume(x== a+b); F = a^2+b^2+2*a*b+a+b+1; simplify(F)

12 years ago | 2

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Answered
Can you turn off all simplifications?
It's a bit tricky. hold(4/6) will not help you because 4/6 -> 2/3 is done by the parser. You will have to define "frozen" forms ...

12 years ago | 1

Answered
Square root of a polynomial over gf
You will have to do it by hand, that is, use polylib::sqrfree and divide all multiplicities by 2. These multiplicities are in th...

12 years ago | 0

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Answered
Factorize transfer function
Don't know how to do it using tf, but you can do syms s Suu = -1.6/((s-4)*(s+4)) Sux = -0.8/((s+4)*(s-4)*(s^2 + 0.1*s...

12 years ago | 1

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Answered
How to solve this equation
This is a recurrence equation and thus has to declared as such using rec(...). eq = evalin(symengine, 'rec(f(x)=h0*f(x)+h1...

12 years ago | 0

Answered
irreducibility test
You have to declare it as a polynomial over GaloisField, e.g. F = evalin(symengine, 'poly(x^2-2, Dom::GaloisField(5^7))) ...

12 years ago | 2

Answered
Problem Solving Symbolic Inequalities
Note that by default solve is in complex mode, i.e., you are looking for all solutions within the complex numbers. Try solu...

12 years ago | 0

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Answered
Symbolic substitution to eliminate variables without solving for the explicit expressions
The second system, too, can be solved. You will have to work on the MuPAD Notebook level or use feval(symengine, ...) though bec...

13 years ago | 1

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Answered
Solving a sine-cosine equation ( Warning: Explicit solution could not be found.)
There is no closed-form symbolic solution for general n, and for given n nobody can say which solutions are between -5 and 5 wit...

13 years ago | 0

Answered
"solve" cannot find analytic solution to a large multi-equation system, unless one is willing to break up the system and solve the parts sequentially
Hi Tamas, this works in newer versions of the symbolic toolbox (R2011a) as we have added some heuristics for systems containing...

13 years ago | 1

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