Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now

# Questions tagged [expression-test]

144 questions
Filter by
Sorted by
Tagged with
17k views

### 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 ...
3k views

### _?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 <...
577 views

### 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 ...
348 views

### 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 ...
295 views

### Which second arguments is VectorQ/MatrixQ/ArrayQ optimized for?

VectorQ and similar functions (MatrixQ, ArrayQ) treat certain second arguments specially. ...
9k views

### 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 ...
1k views

### 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 <...
721 views

### 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 ...
3k views

### 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 ...
3k views

### 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.
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 ...
3k views

### 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 ...
377 views

### 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 ...
3k views

### 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. ...
1k views

### 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 ...
240 views

...
223 views

### A bug in the overloading of MemberQ and FreeQ for Association?

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 ...
1k views

### 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, ...
1k 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 ...
230 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: ...
143 views

### 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? ...
667 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 ...
980 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: ...
232 views

### 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. ...
467 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 ...
444 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 ...
223 views

### ValueQ returns false positive for one argument type only

I'm seeing some perplexing behavior from ValueQ in 10.3. Consider: ...
358 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 ...
2k views

### 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: ...
758 views

### 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. ...
1k views

...
593 views

### Difficulty understanding difference between == and ===

After doing this: ...
15k views

### 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 ...
631 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. ...
302 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 ...
331 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. $H^\dagger=H$) ...
649 views

### TrueQ returning False on true statement

Why does TrueQ return False on the following? TrueQ[Log[2]/Log[8] == 1/3] (* False *) ...
197 views

### 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 ...
116 views

### 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: ...
194 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: ...
755 views

### 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 ...
1k views

### 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 ...
175 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 (...
292 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 ...
511 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 ...
155 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 ...