For questions about symbolic computation, as opposed to numerical computations.
1
vote
1answer
50 views
Calculate angle between skew vectors
I want to use Mathematica to calculate the angle between two vectors (say a and b) that don't lie in the same plane. The vectors ...
4
votes
1answer
200 views
estimation of values using NMaximize over symbolic array entries
I'm trying to generate instances of a dataset that satisfy specific conditions, based on the following equation:
Each of four non-zero terms (term 1, A; term 3, B; term 4, C; term 5, D) is a scalar. ...
1
vote
1answer
63 views
Save and use results of LinearSolve for symbolic large system (28 equations)
I need to solve system of 28 linear equations, for 28 variables, symbolicly.
The coefficient matrix is sparse, and is composed from 8 parameters (symbols).
After that I need to use 6 of the variables ...
1
vote
1answer
39 views
How to change the integral variable and integral upper/lower limit?
I am dealing with the symbolic operation of taking the antiderivative, e.g., Integrate[f, x] (where $f$ represents a complicated function which cannot return ...
6
votes
2answers
264 views
How do I verify a vector identity using Mathematica?
I am trying to verify well known Frenet–Serret formulas in general setting using Mathematica.
I need to consider a general space curve $r(s)=(x(s),y(s),z(s))$ in $\mathbb{R}^3$ and define its unit ...
2
votes
2answers
108 views
Newbie PDE Question
I downloaded Mathematica trial in order to try to solve a PDE that Matlab symbolic couldn't handle. I don't know all the bells and whistles but going along with online documentation.
I am trying to ...
0
votes
1answer
71 views
Mathematica can't solve system of equations but doesn't show error
I try to solve a system of equations:
...
2
votes
3answers
385 views
How to define constants in Mathematica like c1,c2,c3,…cn?
Manually defining the constants is tedious if the 'n' is large. how to do this?
1
vote
1answer
29 views
From algebraic symbols to symbolic functions
i have a code which gives an output of this kind:
rrr=2*f+1;
Now i define a simple function:
f[x_]:=3*x+2;
How should i do ...
7
votes
2answers
159 views
Issue with Upvalues
I want to introduce two variables (I call them EXt and EXtC, where "C" stands for complex conjugate) which would mimic the behavior of a phase of a complex number. For that, I use the following tags:
...
5
votes
2answers
106 views
Why is $\sum\limits_{k=1}^{100} 0.01 $ different than $\sum\limits_{k=1}^{100} \frac{1}{100}$?
Why does evalutating $\sum\limits_{k=1}^{100} 0.01$ not result in 1?
What I get is 1.0000000000000007.
I know that the number 0.01 in binary results in an infinite sequence of zeros and ones, which ...
0
votes
0answers
36 views
How can I simplify expressions correctly?
the final output of my code gives this expression which i call ttt:
...
1
vote
1answer
18 views
Substitution of expressions for the output
I have a code which gives this kind of output :
W = Sum[v[j]*b[j], {j, 1, 3}];
AA = (v[1]*b[1] + v[2]*b[2] + v[3]*b[3])*2 + 3 ;
I know that if i want to ...
2
votes
1answer
45 views
Unable to use `Solve` to solve simultaneous equations, or use `Maximize` for exact maximum solution
Mathematica has found that the maximum of the following function is negative using NMaximize, but I am trying to prove that the maximum is negative (i.e. that the ...
3
votes
2answers
171 views
Transferring DownValues
I have a code in which I define something like this:
cc[1, 2] = 1;
cc[2, 6] = 12;
cc[3, 7] = 3;
After some manipulation I define a sort of temporary variable ...
0
votes
0answers
69 views
Parametric minimization running forever
I am trying to solve for the minimum distance between a line and a cone, for all possible lines in 3D space. I've formulated this as a call to Minimize, but it ...
2
votes
1answer
53 views
Reassign a value to an array element
I have a very complex code in which I assign a value to an element of an array and then I reassign to it another one. A minimal example:
...
1
vote
1answer
43 views
0
votes
0answers
15 views
Using RegionPlot with NIntegrate causes symbolic evaluation when integrating
I am trying to plot the regions when a certain integral is positive. Because the function has many parameters I am passing the values through two sets of rules, one containing the pair of values I ...
1
vote
1answer
51 views
Simplifying a Sum of Fractions by Removing Fractions in Denominators
I have a sum of fractions of the form $x1 - \frac{(x2 + x3)}{(x4 + x5)} - \frac{(x6 + \frac{x7}{x13})}{(x8 - x9 - \frac{x10}{(x11 + x12)})}.$
How might I simplify it to remove fractions from the ...
1
vote
1answer
60 views
Evaluating the 1st argument of Set
I want to assign a certain value to an element of a tensor. This element is identified by an array obtained from some evaluations, so we fix it. Here i present an oversimplified core part of my code:
...
1
vote
1answer
105 views
Tag Times in Null is Protected [closed]
I've some problems with the error mentioned in the title. Unfortunately, my code is full of subscripts so I'll show it in a photo. In this code the central aspect is to assign a scalar value to an ...
1
vote
1answer
38 views
Strange thing about simplification between product and productory [closed]
Good morning,
I have this strange problem. I have to divide a product of 5 variables by 4 of the 5 variables : $C x_1 * x_2* x_3 *x_4 / (x_1 * x_2* x_3 *x_4)$. Now if I do this I don't obtain only $C$...
0
votes
1answer
61 views
Position for array
how does Positionwork for array? In particular if i have something like this:
...
2
votes
2answers
37 views
Symbolic reduce of augmented matrices with TensorReduce
I am trying to reduce a symbolic matrix expression containing augmented/concatenated matrices using TensorReduce, but it does not behave as expected when transposing an augmented matrix.
I assume the ...
0
votes
1answer
29 views
Conditions on parameters in Reduce
i have a system of equations in which there are two parameters F, G. I choose F,G positive. the code is:
...
0
votes
1answer
42 views
Defining a function on the difference of two inputs
Sorry if this is already on this forum somewhere, I had a look but couldn't find anything. Anyway, I am looking to define a function where the inputs are: a and <...
1
vote
1answer
128 views
DiracDelta convergence in 3D - Cartesian vs. spherical coordinates
Integrating DiracDelta in 3D in Cartesian coordinates works just fine i.e. gives vecf[{x, y, z}]
...
1
vote
1answer
91 views
Why the DSolve stop responding when they solve the system of coupled three differential equations?
I try to solve a system of six couple linear PDF. I applied the Laplace transform method and with some simplifications I retain with the following three coupled ODE
...
2
votes
1answer
37 views
How to declare derivatives of a multivariable function as real in order to get Re and Im part of the expression?
Re and Im work properly, with appropriate assumptions, in the example like this
...
3
votes
1answer
51 views
AsymptoticIntegrate with multiple integration variables?
I wanted to find the asymptotic form of
$$\int_0^1\mathrm{d}x\int_0^1\mathrm{d}y\,\mathrm{e}^{M(x-1/2)^2+M(y-1/2)^2}$$
for $M\rightarrow\infty$. I tried
...
7
votes
2answers
69 views
Finding sub-expressions that simplify larger formula
If I use FullSimplify on a large formula it will consequently return a much smaller expression. However, suppose I notice the simplified expression can benefit from ...
7
votes
2answers
323 views
Evaluate Only Part of a Function
I have a list of functions, each containing none or more of the functions Plus, Times, ...
3
votes
1answer
131 views
differential equation solution with DSolve
I have a problem for my work, I need to calculate this diff. equation
I have,
...
1
vote
1answer
48 views
Replacing one of the integrals in the multiple integral with an analytical solution
Problem consist in simplifying complicated multiple numerical integral, where I know analytical solution for a subset of them. Integrand is of the form
...
3
votes
1answer
120 views
Analytically solving of two coupled second order nonlinear ODEs
I have two coupled non linear second order differential equation.
...
2
votes
1answer
52 views
Fourier Transform of a symbolic expression
Hello I would like to do the Fourier Transform of
H1'[t - L2[t]/c - L2primo[t]/c]
I know that its transform has to be:
...
1
vote
0answers
44 views
Finding symbolic series coefficients
Is there any way to get the symbolic form of a series? For simple series this seems possible e.g.
SeriesCoefficent[Exp[x],{x,0,n}]
tells me that the general ...
5
votes
1answer
61 views
DiscretePlot Giving Incorrect Answer
I know similar questions have been asked before about bugs in Integrate, but I'm not sure what the particular problem is here (and whether or not there is indeed a bug). When I perform the integral:
...
4
votes
2answers
88 views
Power Function and Non Commutative Multiply
I'm trying to figure out the best way to define a Power function for non commutative multiply that retains some of the regular features of the ordinary power function. As of now, what I've been ...
1
vote
0answers
42 views
Add operator symbols to matrices in Wolfram [closed]
I am working with the matrices of the form $u = \begin{pmatrix}Y &y\\0 & Y\end{pmatrix}$, and I have an operator $a$ such that $au=\begin{pmatrix}Y & ay\\0 & Y\end{pmatrix}$. Since y ...
2
votes
1answer
39 views
Creating a function that differentiates rational functions
I want to create my own differentiation function Derivada. So, I already set some properties like:
...
7
votes
2answers
93 views
Mathematica Not Interpreting Free Parameters Correctly
Forgive me if this has an obvious answer, but I've run into seemingly the same problem in a few different contexts now. When I evaluate expressions using different variables, all of which show up as ...
3
votes
2answers
47 views
Using Symbolize to Convert Multiple Variables at Once
So, I have created a list of subscripted and overdotted variables that I would like to symbolize, so I run them through a for loop. Seems to me that this would work? Any help is appreciated.
...
1
vote
0answers
42 views
Symbolic differentiation on a function of matrices and vectors
Let $I_t$, $I$, $V$, $Z$ be vectors and $R$, $B$, $P$, $A$, $\mathcal{K}$, $\mathcal{P}$ be some matrices such that
$$ \begin{eqnarray}
S&=&-(R I+B^\top V)^\top \mathcal{R}(R I+B^\top V)
...
1
vote
1answer
91 views
How can I solve a certain complicated second-order PDE?
I am trying to solve the following complicated second-order PDE
...
5
votes
3answers
180 views
2
votes
1answer
44 views
Maximize with matrices
How do I use maximise with an arbitrary sized symbolic matrix?
e.g for a small matrix it is fine to write it out,
...
0
votes
2answers
64 views
Numerical solution of complicated trigonometric equation
I have the following equation to numerically solve for \[CurlyPhi] as function of $k$ and $x$. $k$ is normally between $-\pi\leq k\leq\pi$.
...
1
vote
1answer
62 views
Symbolically solving a complicated trigonometric equation
I want to solve a trigonometric equation involving a few sine functions, for an argument of sine function.
The equation in its ...
