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

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0answers
20 views

Multiple Constrained Sum

I would like to ask if someone knows how to speed up this code, or write an equivalent one in order to perform a multiple summation. The variables a_i are to be ...
1
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1answer
77 views

How to assert that a list of variables is real in a nice and clean way

You can use the function Element to say e.g. $x,y,z\in\mathbb{R}$ via Element[x | y | z, Reals]. Now if I have a list of ...
2
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1answer
51 views

Mathematica does not distribute conjugation when used with Assuming sometimes?

If I input: Assuming[$x_{-} \in$ Reals, FullSimplify[Conjugate[$e^{i x_1}x_2$]]] Then the output is: $e^{-ix_1}x_2$ As it should be. And if instead I do: Assuming[$x_{-} \in$ Reals, ...
0
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1answer
67 views

How to disqualify a rule [closed]

Executing this line Assuming[x < 0, x -> 10] Expected output: False Say x -> 10 is a root of a polynomial ...
0
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3answers
74 views

Identify a scalar, a list

I have a symbolic scalar m2 and a symbolic list (representing a 3x3 matrix) A. I want a function which does something like: ...
0
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0answers
33 views

Need help with solving inequality under assumptions

I seriously need help for my research. I need to solve an inequality with several assumptions. I tried many times with Reduce but it did not work out properly. Sometimes the results I get are simply ...
3
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1answer
88 views

How to tell Mathematica that my variable is a scalar

In my calculations I have these combinations PauliMatrix[1].f PauliMatrix[2] where f is a scalar function. The result is as ...
2
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1answer
166 views

How to properly interpret a seemingly contradictory result in Mathematica?

I have a problem with interpreting the results of my notebook outputs. It is important that I do not err with the interpretation. Here is the full input: ...
-1
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1answer
64 views

Find a minimum value which satisfies an equation

I have to find a minimum value of "a" which makes x=-a+b+c, y=-a+b+c^2 positive where a>1, 0 ...
0
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1answer
83 views

Integral evaluation error

I have the following integral that I wish to evaluate using Mathematica: ...
0
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1answer
75 views

Solving differential equation with Variable constans?

How do I solve the following differential equations using Mathematica under the assumptions: If Abs[r[t]]<50 ->A=0.5;B=2; AND ...
1
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0answers
61 views

How can I force the assumption that a symbol is a vector of n zeros

Using $Assumptions = Element[n, Integers] && Element[a, Vectors[n, Reals]] I can assume that a is a n-dimensional vector of Reals. How can I assume that ...
0
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1answer
58 views

Why is zero times vector of reals not zero?

Using the following global assumptions $Assumptions = Element[n, Integers] && Element[a, Vectors[n, Reals]] && b == 0 && Element[c, Reals] ...
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1answer
62 views

Using Assumptions in Expressions that Evaluate to be Elliptic Integrals

I have the following integral that I am trying to evaluate in Mathematica: $\int \sqrt{\alpha + m g l \cos(q)} dq$. If $\alpha > m g l$, then the result is a complete elliptic integral of the ...
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1answer
48 views
1
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1answer
47 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 ...
4
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2answers
182 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 ...
3
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2answers
51 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
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1answer
136 views

Mathematica does not help in this integral

I am trying to solve this integral with assumptions: ...
4
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2answers
128 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 ...
1
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2answers
387 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
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1answer
71 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
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1answer
50 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 ...
1
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2answers
74 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]] ...
2
votes
1answer
190 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 ...
2
votes
2answers
106 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 ...
4
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1answer
76 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
114 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
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1answer
63 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
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1answer
95 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
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1answer
61 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
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0answers
60 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
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1answer
103 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
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1answer
53 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 ...
1
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2answers
99 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 ...
2
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0answers
67 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
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0answers
81 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
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1answer
83 views

Inconsistent results for Integrate depending on irrelevant assumptions

I stumbled across this amusing issue today when doing some definite integrals: ...
0
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0answers
79 views

Piecewise functions Integration with symbol

I want to integrate one piecewise functions as following, ...
7
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3answers
127 views

Unknown function with arbitrary arguments assumption

Is it possible to define an assumption like this: $Assumptions=f[__]>0 So that: ...
0
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1answer
135 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
229 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
168 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 ...
3
votes
1answer
121 views

How to use Assuming and If together?

I would like to compare variables t and u and print either Yes or ...
1
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1answer
68 views
5
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1answer
99 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 ...
4
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1answer
353 views

Can I check if an expression is positive using assumptions?

I have the following notebook: ...
1
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0answers
65 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
294 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 ...
3
votes
2answers
77 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, ∞}]] ...