Questions about the function Assuming[], the $Assumptions system variable, and the Assumptions option of functions such as Simplify[] and Integrate[].

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2
votes
3answers
539 views

DSolve will not apply assumption m ∈ Integers

I am trying to solve a linear second order ODE using DSolve which involves an arbitrary integer m. ...
1
vote
1answer
40 views

Limits with assumptions

I have an example where Mathematica is not able to compute limits in a function restricted to assume that the input parameter is Real. I don't understand why this is so. 1. Could someone explain why ...
1
vote
2answers
72 views

VectorFieldPlot Assumptions - restricted domain

I would like to plot the 2-D vector field: VectorFieldPlot[{ x/Sqrt[x^2 + y^2], y/Sqrt[x^2 + y^2]}, {x, -5, 5}, {y, -5, 5} ] but I encounter zero division at ...
1
vote
4answers
2k views

How to take conjugate of a function?

Naïvely this is what happens and it obviously is not helpful! ...
4
votes
2answers
165 views

Assumptions with patterns

I want that Mathematica assumes every symbol like Subscript[s,i] to be evaluate as a real and positive number. I have tried ...
4
votes
1answer
129 views
2
votes
1answer
147 views

Is there a way to simplify a symbolic expression at assignment, once-for-all?

I have a series of symbolic function calls that could be greatly simplified using some assumptions. I think I would like for these assumptions to be used in the definition of the function so that they ...
3
votes
2answers
47 views

Simplify with assumption of unknown function [duplicate]

I have an unknown multivariate function entry[x,y,z], which is positive. Then how to get FALSE and entry[1,2,3] in the following evaluations? ...
4
votes
2answers
118 views

Well-defined symbolic integral leading to ConditionalExpression

I would like to determine a closed-form expression for the following symbolic integral $$ \int_{-1/2}^{1/2} \!\!\!\! \mathrm{d} x \int_{-1/2}^{1/2} \!\!\!\! \mathrm{d} y \, \frac{1 + b x + c y}{1 + e ...
0
votes
2answers
61 views

Defining the domain of positive real numbers

I am trying to solve an equation by assuming that all the variables are real and strictly positive. I can use the keyword Reals for the argument ...
0
votes
1answer
57 views

Assumptions and Conditions in Integrate Function in Mathmatica

I was trying to Integrate the gravitational potential at r = x produced by a uniform sphere positioned at the origin. I wrote the following code: ...
1
vote
1answer
40 views

Simplify CubeRoot of meter cubes

Why Mathematica doesn't simplify CubeRoot of meter cubes to meters? r = Quantity[10, "Meters"]; v = 4/3 r^3 Pi; CubeRoot[% * 3/4 / Pi] returns ...
2
votes
2answers
88 views

Simplifying expressions with Abs

I have a long expression which seems really complicated due to some Abs[] terms that should be simplified. However, even with the right assumptions, the expression ...
1
vote
2answers
58 views

Abs[Sin[4a]] not equal to 2Sin[2a]Abs[Cos[2a]] for a in [0,\pi/2]

I have a long expression which is not fully simplified because Abs[Sin[4a]] is considered different from 2Sin[2a]Abs[Cos[2a]] ...
4
votes
1answer
66 views

Problem with Simplify, Sqrt, and Set: What's going on?

I am having some trouble getting Mathematica to simplify an expression of the form Sqrt[x]*Sqrt[1/x], where x>0. The problem is that x is assigned to some complicated form by the time Mathematica ...
1
vote
3answers
102 views

IntegerQ returning False despite setting Assumptions

Why does the following not return True? Assuming[z ∈ Integers, IntegerQ[z]] False I tried this on a fresh session of ...
1
vote
1answer
51 views

How to make strong assumptions?

Or put in another way, how to make a variable behave as it belongs to a specific domain, even outside the use of simplify or other commands alike? For example: ...
1
vote
1answer
63 views

Assuming variable is plus or minus 1

I have a long calculation that I am doing, which involves a particular variable h, which in the end, is either +1 or -1. (I would like a general result that is true for both cases.) Since h only ...
1
vote
1answer
56 views

Defining a matrix with the symmetry Transpose[A(q)]=A(-q)

I am trying to construct a symbolic matrix with the following property- $$ \left(D_{3\times3}(q)\right)^T = D_{3\times3}(-q) $$ Note that for $q\in \mathbb{R}$, $D(q)$ would be hermitian. So far i ...
5
votes
0answers
54 views

SumConvergence fails in version 10

SumConvergence[(-1)^(n + 1) ((Cos[n^2] + Sin[n + 2])/7^n), n] Mathematica fails to provide a result (true/false) but wolfram alpha works. What should I do ? It ...
2
votes
1answer
77 views

Simplifying conditional expressions using assumptions does not work

I have a conditional expression f[x_] := x /; x ∈ Reals This works fine for normal numbers and symbols, e.g. ...
0
votes
1answer
49 views

Assuming: what am I doing wrong? [duplicate]

Why doesn't this simple line work? Assuming[Element[#, Reals] & /@ {x}, Reduce[x^4 == 1]] (* x==-1||x==-I||x==I||x==1 *) I'm trying to do something a little ...
2
votes
0answers
58 views

How do I apply assumptions to a module (or any CompoundExpression)?

Edit: I am looking for a way to apply assumptions to all expressions contained in a compound expression. For example, ...
0
votes
0answers
46 views

Using assumptions when calling Simplify from Collect

I am quite new to Mathematica, so please be patient ;) I have a very long equation that I have to sort for powers of a variable called e and that I want to ...
7
votes
1answer
79 views

Inconsistent results for Integrate depending on irrelevant assumptions

I stumbled across this amusing issue today when doing some definite integrals: ...
0
votes
0answers
55 views
7
votes
3answers
111 views

Unknown function with arbitrary arguments assumption

Is it possible to define an assumption like this: $Assumptions=f[__]>0 So that: ...
19
votes
2answers
843 views

Optimization with assumptions

I have the following problem, when I am trying to optimize function with pre-defined assumptions. I am using Mathematica 8 and I wrote the following simple code ...
0
votes
1answer
106 views

How do I declare that a variable represents a real number?

How do I tell Mathematica that a variable is a real number. I searched for this question here and in Google and nothing that was suggested seems to work for me. I must be missing something. My code is ...
5
votes
0answers
191 views

Integrate wrong for absolute value of trig function

I was trying to get $\int_0^1 \lvert \cos(2 \pi k x) \rvert \,\mathrm{d}x$ for $k \in \mathbb{Z}$, and was surprised by the result (using Mathematica 10.0.1.0): ...
5
votes
3answers
156 views

Assuming reals of unknown variables in a Matrix valued function

I am trying to write a generic matrix valued function in a package, of the form: f[matrix_] := Module[...] My problem is that I want to accept any matrix, but ...
9
votes
1answer
240 views

Limit of sequence of functions behaving strange

I'm trying to determine the limit of the sequence of functions $$f_n(x)=\left(\frac{1}{\pi}\arctan(n x) + 1/2\right)^n. $$ I define ...
1
vote
1answer
54 views

How to use many global assumptions [closed]

I would like to use many global assumptions. Say I have two global assumptions. $Assumptions = 0 < a < 1 $Assumptions = 0 < b < 1 Then I would like ...
3
votes
1answer
106 views

How to use Assuming and If together?

I would like to compare variables t and u and print either Yes or ...
3
votes
2answers
75 views

Why does Assuming[…] work in one case but not in another?

Why does this work Assuming[α > 0 && ϵ > 0 && t > 0, FullSimplify @ Integrate[(z^2 Exp[-α t (z^2 + ϵ)])/(z^2 + 1), {z, 0, ∞}]] ...
5
votes
1answer
85 views

Problem with general assumptions

I hope I am not to redundant with my questions. As part of solving a physical problem, I want to assume once and for all that all my variables and parameters are real, positive and finite. Is it ...
1
vote
1answer
252 views

Appending to $Assumptions - Error “Nonatomic expression expected” [closed]

I need to use lots of assumptions in my code. Therefore I put them into the $Assumptions variable. When I do it like this, all is well: ...
1
vote
1answer
49 views

PiecewiseExpand doesn't take all kind of assumptions

Running PiecewiseExpand[expr, assum] does not work with all kind of assumptions. For example, the following line will not split the expression with absolute values in the chambers, considering m1=m2. ...
0
votes
0answers
58 views

Getting long complex-valued integrals when simpler real-valued expressions exist

I have a long list of real-valued functions I'd like to integrate symbolically. For many of them, Mathematica gives me results with long complex-valued expressions involving weird functions such as ...
14
votes
3answers
256 views

Why does Mathematica simplify $x/x\to1$?

If I enter x/x, I get 1. Such behavior leads to this: Simplify[D[Sqrt[x^2], x, x]] 0 ...
0
votes
0answers
63 views
0
votes
0answers
32 views

Assumptions for simplifying a long equation

I'm having trouble combining assumptions with the execution of Simplify in a long equation. The idea is to separate imaginary and real parts of a complex equation. ...
0
votes
0answers
22 views

Assumption for all the notebook [duplicate]

I would like to know how to fix an assumption over a variable that will be fixed for all notebook. For example a>0 in all the notebook.
0
votes
0answers
63 views
0
votes
2answers
109 views

How to use Assumptions in a Series Expansion

I want to series expansion the expression $\frac{1}{2} \left(e_1+e_2-\sqrt{e_1^2-2e_1e_2+e_2^2+4V_{12}^2} \right)$ up to second order in $V_{12}$ using the assumption $e_1>e_2$. So I tried ...
2
votes
0answers
142 views

Computing a sum

I'm trying to make Mathematica compute this sum: Sum[(-1)^k (n - k)^2 Binomial[2 n, k], {k, 0, n}] As is, I get an awful formula: ...
1
vote
3answers
92 views

FullSimplify assumptions for function body

I'd like to pass an assumption to FullSimplify so whenever it gets a function that is squared and square rooted would return me only the function body, without ...