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Questions about the function Assuming[], the $Assumptions system variable, and the Assumptions option of functions such as Simplify[] and Integrate[].
1
vote
How to use assumptions without Simplify[]?
}, Simplify @ Conjugate[e]],
DownValues[Conjugate] = {}
];
Protect[Conjugate];
)
Then, turn on conjugate simplification:
SetConjugateSimplification[True]
Now, Conjugate will use assumptions … specified with $Assumptions or Assuming:
$Assumptions = c10 ∈ Reals;
Conjugate[c10]
c10
Restore the usual Conjugate behavior:
SetConjugateSimplification[False]
Another possibility is to use …
5
votes
Accepted
Laurent Series with Symbolic Powers
One possibility is to just replace your variable with one whose powers are all explicit integers, and then use Series:
e = PowerExpand[
a^(-c2)/((a*c1)^(c2) + c3) /. a -> z^(1/c2),
Assumptions …
3
votes
Simplifying inequalities with exponents
I think using Reduce would be a better approach, although it's not completely straightforward:
Reduce[x^a < 1 && a > 0 && x > 1, Reals]
False
(updated with another approach using Resolve)
Ano …
3
votes
Accepted
How to Integrate the Derivative of a function with Assumptions on the function?
You could try using DSolveValue. First, define your sum using inactive integrals:
h[α_] := Inactive[Integrate][x g'[x],{x,0,α}] + Inactive[Integrate][α g'[x],{x,α,∞}]
Even though the integrals are …
2
votes
Solving for positive square root of an equation, using assumptions
Solve doesn't make use of Assumptions. Also, your first assumption doesn't mean anything. …
2
votes
Accepted
Reevaluating an expression when Assumptions have changed
You need to use Update to tell Mathematica that hidden changes have been made that can affect results:
THM=TensorDimensions[M];
Assuming[Element[M,Vectors[n]],THM]
TensorDimensions[M]
Using Up …
1
vote
Accepted
Clarity of assumptions in PowerExpand
On the other hand, you can use explicit assumptions for x1 and x2 only:
PowerExpand[Sqrt[x1^2] + Sqrt[x2^2] + Sqrt[x3^2], Assumptions->x1<0&&x2>0]
-x1 + x2 + E^(I π Floor[1/2 - Arg[x3]/π]) x3
In … On the other hand, if you include a non-default Assumptions option, then the output of PowerExpand will be correct (for the given assumptions). …
4
votes
Accepted
Solve yields complex Root even if the domain is Reals
ToRadicals supports the undocumented option Assumptions. … Making use of this option gives:
sol = Solve[x^3==a^2,x,Reals]
ToRadicals[sol, Assumptions -> a>0]
{{x -> Root[-a^2 + #1^3 &, 1]}}
{{x -> a^(2/3)}} …
7
votes
Accepted
Representing number domain by a symbol
Per the documentation you can use Esc ints Esc to enter the StandardForm symbol for Integers
7
votes
Defining the domain of positive real numbers
New in Mathematica 12 is PositiveReals (and others like NonNegativeIntegers, etc):
Solve[x^2 == 1, x, PositiveReals]
{{x -> 1}}
5
votes
Accepted
How to 'define' value in Assumptions but not let Simplify replace it?
One possibility is to mimic the behavior of symbolic constants like Pi, E, etc:
N[x, _] ^= 4;
NumericQ[x] ^= True;
Then:
Sqrt[x^2]
x
without even using Simplify.
3
votes
Accepted
Triple integral: How do I include assumptions and conditions?
The region of integration is:
reg = ImplicitRegion[0 < y < a && 0 < x < z && 0 < z < y, {x, y, z}];
Using this region in Integrate:
sol = Integrate[Exp[(a-x)^3], {x, y, z} ∈ reg, Assumptions -> a > 0] …
4
votes
Accepted
Taking residues with integer assumptions?
You could use SeriesCoefficient instead:
Assuming[n ∈ Integers && n>1,
Simplify @ SeriesCoefficient[
Exp[x] x^(-1-n),
{x, 0, -1}
]
]
1/n!
1
vote
How to integrate assuming some integrals are named constants?
Here's an unorthodox approach. Since $\int_{-\infty }^{\infty } f(x) \, dx$ is just FourierTransform[f[x], x, 0] (up to suitable FourierParameters), you could use UpValues to teach Mathematica about F …
21
votes
Accepted
Logarithm of exponential
Another method is to use PowerExpand:
PowerExpand[Log[E^a], Assumptions -> True]
a + 2 I π Floor[1/2 - Im[a]/(2 π)]
Addendum
As an aside, Log behave exactly like ArcSin here:
ArcSin[Sin[x]] … Pi/2 < x < Pi/2]
x
For larger domains, Simplify doesn't work:
Simplify[ArcSin[Sin[x]], 0 < x < 2 Pi]
ArcSin[Sin[x]]
Again, using PowerExpand is useful:
p = PowerExpand[ArcSin[Sin[x]], Assumptions …