symbolic-math

问题 I want to use symbolic symbol to solve a system of linear equation. So I prepare the following code. A=[1,2;3,4]; % syms x x=sym('x_%d',[2 1]); eqn=A*x==[1;2]; result=solve(eqn,x) Interestingly, it works, but when I read the variable result, it gives a 1X1 struct with x_1 and x_2 are 1X1 sym. But what I expect get should be 2 real values, why? Could someone explain it? Remark: do not want to use A^-1*[1;2] to obtain the answer. 回答1: If you set the output to single variable solve returns a

问题 I have equations defined like f<-"x^2" and g<-"y^2" . I want to obtain equation z like z<-(x^2)*(y^2) . 'Class(f)', 'class(g)' and 'class(z)' values doesn`t matter for me. I tried this: > f<-"x^2" > g<-"y^2" > z<-f*g I got: Error in f * g : non-numeric argument to binary operator<br/> I tried multiplying f<-expression(f) and g<-expression(g) with no result. I tried also: > f<-function(x) x^2 > g<-function(y) y^2 > z<-function(x,y) f*g > z<-parse(text=z) I got: Error in as.character(x) :

问题 I have a multivariable symbolic expression say c = x^2 +y^2 + z^2 using matlabFunction(c) returns ans = @(x,y,z)x.^2+y.^2+z.^2 I can't input this into fminsearch (because it has multiple scalar inputs right?). How can I change the format of the output so it takes something that fminsearch actually allows, something like @(x)x(1)^2+x(2)^2+x(3)^2 It is feasible to do this manually for 3 variables but not for hundreds. The errors look something like if it helps: Error using symengine?makeFhandle

问题 I have the unit step function: u0:= piecewise([-infinity < t and t < 0,0],[0 < t and t < infinity,1]): Now I want to plot it at some point: T:=1:; plot(u0|t=t-T/2); This works. But when I use a more natural expression: T:=1:; plot(u0(t-T/2)); it simply plots the original unshifted step function. Is there any way to use the more simpler form when plotting the modified step function? 回答1: I believe the reason that what you call the "more natural form" doesn't work, is because u0 has not been

问题 Boolean operation of a Boolean variable on a symbol produces TypeError , but the reverse has no problem: >>> from sympy import * >>> x = Symbol('x', bool=True) >>> x ^ True Not(x) >>> True ^ x Traceback (most recent call last): File "<pyshell#3>", line 1, in <module> True ^ x TypeError: unsupported operand type(s) for ^: 'bool' and 'Symbol' I can do try-catch: try : print True ^ x except TypeError: print x ^ True Not(x) But, for my present task, it is impossible to implement this with try

问题 This is matrix B B = [1 2 0 ; 2 4 6 ; 0 6 5] The result of eig(B) is: {-2.2240, 1.5109, 10.7131} and the characteristic polynomial of B by this link is syms x polyB = charpoly(B,x) x^3 - 10*x^2 - 11*x + 36 but the answer of solve(polyB) is 133/(9*(3^(1/2)*5492^(1/2)*(i/3) + 1009/27)^(1/3)) + ((3^(1/2)*5492^(1/2)*i)/3 + 1009/27)^(1/3) + 10/3 (3^(1/2)*(133/(9*(3^(1/2)*5492^(1/2)*(i/3) + 1009/27)^(1/3)) - ((3^(1/2)*5492^(1/2)*i)/3 + 1009/27)^(1/3))*i)/2 - 133/(18*(3^(1/2)*5492^(1/2)*(i/3) + 1009

问题 I am trying to make lambdify understand to expect more than one type of input using the modules keyword argument. According to the source code of lambdify (http://docs.sympy.org/dev/_modules/sympy/utilities/lambdify.html), this can be done by using lists of the arguments, but i am not able to do so. import sympy from sympy import lambdify x,y=sympy.symbols('x y') from sympy.parsing.sympy_parser import parse_expr func=lambdify(x,parse_expr(exp(x)),modules=["numpy","sympy"]) func(array([3,4]))

问题 I am trying to make lambdify understand to expect more than one type of input using the modules keyword argument. According to the source code of lambdify (http://docs.sympy.org/dev/_modules/sympy/utilities/lambdify.html), this can be done by using lists of the arguments, but i am not able to do so. import sympy from sympy import lambdify x,y=sympy.symbols('x y') from sympy.parsing.sympy_parser import parse_expr func=lambdify(x,parse_expr(exp(x)),modules=["numpy","sympy"]) func(array([3,4]))

问题 I'm trying to compute eigenvalues of a symbolic complex matrix M of size 3x3 . In some cases, eigenvals() works perfectly. For example, the following code: import sympy as sp kx = sp.symbols('kx') x = 0. M = sp.Matrix([[0., 0., 0.], [0., 0., 0.], [0., 0., 0.]]) M[0, 0] = 1. M[0, 1] = 2./3. M[0, 2] = 2./3. M[1, 0] = sp.exp(1j*kx) * 1./6. + x M[1, 1] = sp.exp(1j*kx) * 2./3. M[1, 2] = sp.exp(1j*kx) * -1./3. M[2, 0] = sp.exp(-1j*kx) * 1./6. M[2, 1] = sp.exp(-1j*kx) * -1./3. M[2, 2] = sp.exp(-1j

问题 I've tried to use a script that evaluates the Pochhammer symbol (rising factorial) in Matlab, but it fails to evaluate pochhammer(x,n) whenever x is a negative number even though the expression is valid when x is negative (Wolfram Alpha and Mathematica give answers for Pochhammer(-3,2) ). Can anyone help me get pochhammer working in Matlab for negative arguments? 回答1: I assume that you're referring to this Pochhammer function. Note that pochhammer (not capitalized) is part of MuPAD, which is