Questions tagged [expression-test]

142 questions
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How to check if a 2D point is in a polygon?

Background: I use code from An Efficient Test For A Point To Be In A Convex Polygon Wolfram Demonstration to check if a point ( mouse pointer ) is in a ( convex ) polygon. Clearly this code fails for ...
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_?NumericQ equivalent for lists

A few months ago I got a simple answer (see: 1 ) to the question of how to force numeric evaluation during use of functions such as NMinimize[] - namely the use of <...
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Is there a GraphicsPrimitiveQ (or a complete list of Heads of graphics primitives)?

For various reasons related to workflow associated with creating figures for journals, I am creating functions that will accept graphics primitives and a set of options and spit out a ...
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Does Mathematica store hidden information for matrix objects?

Bug introduced in 10.0 and fixed in 10.2.0 I found a case where calling one built-in function (HermitianMatrixQ) for a given matrix changes the behavior of another ...
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Which second arguments is VectorQ/MatrixQ/ArrayQ optimized for?

VectorQ and similar functions (MatrixQ, ArrayQ) treat certain second arguments specially. ...
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How to check if an expression is a real-valued number

What is a simple, fast way to test whether an expression is a real-valued number? I ask since there is no RealQ function. If we call this test ...
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Why no RationalQ or RealQ?

Interesting pattern came up as I go through the homework replies of my students. Why is there no RationalQ or RealQ? We have <...
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Implementing a safe ValueQ that does not evaluate its argument

Mathematica has a built-in function ValueQ. Quoting the docs, ValueQ[expr] gives True if ...
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How do you check if there are any equal arguments(even sublist) in a list?

I would like to set up a function which has to return True if at least two arguments of a given List are equal. So if I give {1,4,6,2} to the function it has to ...
1k views

Why does Mathematica claim there is no even prime?

I wonder if this is a bug, or if I'm misunderstanding something: Exists[n, EvenQ[n] && PrimeQ[n]] // Resolve (* ==> False *) So if I interpret this ...
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Determine whether some expression contains a given symbol

Given a symbol t and an expression expr, how can I determine whether or not the symbol t ...
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Fastest square number test

What is the fastest possible square number test in Mathematica, both for machine size and big integers? I presume starting in version 8 the fastest will be a dedicated C LibraryLink function.
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How can I test properties of a symbol from the string name without the symbol completely evaluating

Suppose I have a few symbols, one of which has a value: {abc1, abc2 = 5, abc3}; I can use Names to get the list of names, as ...
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Checking if a point is in a convex 3D polyhedron

Extending from these questions How to check if a 3D point is in a planar polygon? and How to check if a 2D point is in a polygon?. I'm trying to do this to render specific shapes made up of spheres. ...
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How to check if a vector is an eigenvector of a matrix using mathematica?

Here is a vector $$\begin{pmatrix}i\\7i\\-2\end{pmatrix}$$ Here is a matrix $$\begin{pmatrix}2& i&0\\-i&1&1\\0 &1&0\end{pmatrix}$$ Is there a simple way to determine ...
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Is it OK that SameQ considers expressions identical, although they have different structure?

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Bug introduced in 10.0.0 and fixed in 10.1.0. While answering Pattern match for nested Association I came across behavior of MemberQ and ...
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How do I get Mathematica to return a function call unevaluated?

How do I get Mathematica to return a function call (conditionally) unevaluated? I expect this may use the slightly-mysterious Hold function. As a toy example, ...
956 views

Checking if a word exists

Probably the simplest way to check a word if it exists is to use DictionaryWordQ[] DictionaryWordQ["color"] True But it ...
225 views

IsomorphicGraphQ fails to recognize that two empty graphs are identical

Bug introduced in 9.0.1 or earlier and fixed in 11.0.1 Consider the following two graphs: ...
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Why is IsomorphicGraphQ so very slow (in this instance)

Bug introduced in 10.0 or earlier and persisting through 12.0.0 Can someone explain why the following code does not complete within a reasonable time? ...
659 views

Better way to test that a matrix is upper-triangular?

Today, I got to thinking about how to test that a matrix was upper-triangular. So I had a try at it. Algorithm $\quad \quad a_{ij}=0$ Or $i \leq j$ $\Rightarrow$ $True$ My solution is ...
883 views

Unexpected slowness checking for empty list?

I thought I had a firm understanding of the differences between Equal and SameQ, but this has me puzzled: ...
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How can one write a robust ListableQ function?

I would like to have a test that determines if a particular function is Listable. In the case of Symbols this is merely a matter of checking Attributes. ...
442 views

Why is an empty list not tested by VectorQ?

I am a bit amazed by this behavior of VectorQ[ expr, test ]: VectorQ[ {}, NumberQ ] True It seems that the test itself is ...
437 views

Why does Assuming[x > 0, TrueQ[x > 0]] return False?

Assuming[x>0,TrueQ[x>0]] should, as I understand it, test TrueQ[x>0] after assuming ...
220 views

ValueQ returns false positive for one argument type only

I'm seeing some perplexing behavior from ValueQ in 10.3. Consider: ...
349 views

About shorthand notation for conditional pattern (Paul Wellin “Essentials of Programming in Mathematica”)

I am reading Paul Wellin's "Essentials of Programming in Mathematica". Mr. Wellin wrote the following in his book: There is a convenient shorthand notation for conditional patterns that is ...
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Evaluating an If condition to yield True/False

I would like to decide whether an option passed to my custom function has the value Automatic or something else. This is my attempt: ...
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Test if a list is a constant integer multiple of another list

I have a list of lists, and I want to eliminate all the lists that are constant integer multiples of another list. My initial approach was to divide the lists using nested tables. ...
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Difficulty understanding difference between == and ===

After doing this: ...
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How to detect if a sequence of integers is consecutive

I'm not a math-guy really (a programmer actually) and this is my first question. And excuse me if I can not explain my problem good. The problem is I have a sequence of integers and I want to detect ...
626 views

How does Mathematica decide that Log[2,8] is integer?

At school we learned that $\log_b(x)=\log(x)/\log(b)$, which is implemented in Mathematica as Log[b, x], but the results are different. ...
271 views

Test for non-numeric variables

I have a table, testdata, with numeric and non-numeric data. testData = {{1, 2, 3, no, 5}, {5, 6, 7, 8, 9.1}, {1, y, y, n, n}}; I can locate the positions of ...
321 views

UnitaryMatrixQ function not returning true for a unitary matrix

So I know this matrix is unitary. It's a well proven fact in quantum mechanics and you can even check for yourself on pen and paper, Heres a quick proof: Assume $H$ is hermitian (i.e. $H^\dagger=H$) ...
582 views

TrueQ returning False on true statement

Why does TrueQ return False on the following? TrueQ[Log/Log == 1/3] (* False *) ...
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1 is not the SameQ as Null, but why might 1 be Equal to Null?

The command SameQ[1, Null] returns False which is what I would expect, but the command ...
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Ordering real numeric quantities

Suppose I want to have a function (call it NLess) that given two real numeric quantities, a and b, it returns True if a is smaller than b, ignoring precision. Here are some test cases: ...
190 views

Bug in PositiveDefiniteMatrixQ?

Fixed in 10.1.0. Exists in at least 9.0.1 -- 10.0.2. This seems like a bug in PositiveDefiniteMatrixQ to me: ...
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How to check is there any negative term in a large list?

I want to check if a data set of size $10^{10}$ contains any non-positive elements. Positive[Name of dataset] returns a list of ...
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A hack for aggressive type-checking?

I tend to like programming in a style where I can be very explicit about the types of expressions. While Mathematica isn't and shouldn't be a strongly-typed language like Haskell, I think it would ...
172 views

Can anyone guess what InternalRadicalMemberQ does?

There is an undocumented function InternalRadicalMemberQ which takes two arguments. But whatever input I try for the two arguments, it seems to crash the kernel (...
287 views

Is there a defined priority for pattern matching?

If you define a function g, like so: g[x_?EvenQ] := "even" g[x_?NumberQ] := "number" why will Mathematica always return ...
451 views

Using OddQ and EvenQ in piecewise functions: Buggy?

I was trying to evaluate a sum over a piecewise function, not unlike this example. However, my piecewise function needed to be defined differently for even and odd ...
105 views

Why does SameQ act inconsistently with Images wrapped in {} versus not?

Take an Image that is displayed in a GraphicsBox, e.g. the result of ...
142 views

Mystery with ValueQ

Consider the following ClearAll[jd]; ValueQ[jd] We expect False and get it. Now consider ...
146 views

SameQ for unsorted lists

I have to compare two or more lists and check if they are the same, but their elements can be in different position. For instance ...