# Tagged Questions

108 views

### time complexity of MemberQ

I was rather surprised that the operator form of MemberQ takes a form as its argument. I looked for the operator form thinking that repeated testing for elementhood in a given "set" is a common need ...
65 views

### Rapidly testing for exact vs. inexact expressions

Is there a fast function "ExactExpressionQ" to test whether an expression is exact vs inexact? I'm looking for something like ...
47 views

### Using ValueQ to test whether “hash” key exists fails when key is given as variable

Please ignore ^^^ possible duplicate (raised by me). The solution doesn't cover my case. I'm trying to implement a simple hash table according to this top answer at "Is there HashTable structure in ...
39 views

### Testing for nontrivial evaluation

How can I tell programmatically if a function has evaluated in a nontrivial way? I'd like to do, essentially, something along the lines of f[x]===HoldForm[f[x]], a ...
249 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 ...
213 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 ...
60 views

### Expression in mathematica [closed]

i have an expression: n*Subscript[e,3] Subscript[e,4] Subscript[e,7]...*Subscript[e,k]*Subscript[e,k] I would evaluate it such as return n*Subscript[e,3*4*k*k+1] ...
138 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 ...
61 views

### Configurable tolerance for numerical equality?

In standard C++ the double values for 1. + 1.2*^-16 and 1. are not considered equal. But in Mathematica, I get the following: ...
110 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. $H^\dagger=H$) ...
277 views

### How to test whether a function is positive over the entire range of an interval?

I would like to test whether a function is positive over a given interval. Say I have f[x_] = -x^3 + x^2 + 7*x and wanted to know whether it is positive for all <...
89 views

### Faster square test for integers

This question was asked already in Jan '12 and the most recent answer is from Oct '12, so it's several Mathematica versions out of date. What is a faster test for whether an integer is a perfect ...
87 views

### Count number of summands?

Consider fun = a+b+c+d/e If we want to get the number of summands, we can use Length[fun], which properly gives ...
519 views

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

After doing this: ...
156 views

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

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

### Picking points in a plane under a curve given by a list

Suppose that I have a set of points in a plane, which range from $x\in [0,20]$ and $y\in[0,10]$, and a curve given by a list of points in the same region: ...
65 views

### Can Mathematica point out why it thinks two symbolic expressions are different?

SameQ checks to see if symbolic expressions are the same. There are some caveats, as pointed out by the answers to: Understanding SameQ What is the proper way to ...
160 views

### IsomorphicGraphQ fails to recognize that two empty graphs are identical

Bug introduced in 9.0.1 or earlier and persisting through 10.4.0 Consider the following two graphs: ...
44 views

### Equality of expressions containing complex numbers [closed]

I am using Mathematica to test the equivalence of symbolic expressions. I run into what appears to be a bug when I test the equivalence of expressions involving an imaginary number taken to a complex ...
98 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 ...
213 views

### ParallelMemberQ

I tried to make a parallel version of MemberQ for use with a large list, but failed miserably in terms of performance. I used Partition to subdivide the list and ParallelMap to perform the MemberQ ...
302 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 ...
201 views

### Nested If statement with unevaluated arguments

I have a list of boolean functions {f1, f2, f3, ...} that take a value and return True or ...
223 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: ...
522 views

### Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
88 views

### Sign of expression with several parameters

Briefly (with thank to all reader) Want to determine the sign in the interval $[0,1]$ of the expression  b (p-1) x^{-p}-\gamma +\eta _1 k_0+\frac{\beta _0 \left(\eta _1+\eta _2-1\...
33 views

### Testing for a vector of all reals [duplicate]

I want to test if an expression is a vector of all reals. I defined RealVector[expr_]:=VectorQ[expr,NumberQ[#]&&(Head[#]===Real)]; Trying this on ...
190 views

### How to properly apply NumericQ or s.th. similar here? - NDSolve inside NMaximize

I wrote a function that numerically solves a given Schrodinger equation and returns replacement rules to obtain the time evolution operator. It looks and is used as follows: ...
240 views

### Understanding SameQ

I am new to Mathematica. So I have read the documentation for comparing expressions in Mathematica and I still don't get the SameQ (===) function. Let me give you a short example: ...
66 views

### How to use MemberQ for such Variables?

This is NOT the desired out come. I want this test to fail: ...
143 views

### How to determine if directories with executable permission and not

I have some directories that have the UNIX executable permission some does not. What tests could I write in Mathematica to test it?
138 views

### IntegerQ and Element Integers give different results in one case

f1[x_] := IntegerQ[x] f2[x_] := Element[x, Integers] Both functions give identical results in everything except for such case: ...
197 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 ...
518 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 ...
261 views

### TrueQ returning False on true statement

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

### Why does pattern test not work in this case to restrict the function parameters?

I was looking at this Q&A about using pattern test (pattern_?test) vs pattern condition (pattern_/;cond) and came across ...
158 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: ...
257 views

### Sum with IntegerQ does not converge

Why does Mathematica return: Sum::div: Sum does not converge. >> when I input: ...
221 views

### Finding similar expressions in list

I have a function that returns to me lists of expressions, like: ...
133 views

### Testing for arbitrary algebraic expression in given variable

I want to test, for example with MatchQ, if the argument of a function is an arbitrary expression in a single or several variables whose names can be assumed to be ...
169 views

### Checking through an expression

I am writing a code that manipulates expressions that contains functions with an arbitrary number of arguments. An example expression is ...
135 views

### Mystery with ValueQ

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

### Why does PolynomialQ[x^n, x] return False?

From what I can see PolynomialQ will return False whenever some exponent is another variable such as here: ...
4k 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 ...
675 views

### Faster way to test if an expression equals zero

I want to test if expressions (mix of variables, functions and numbers) are zero valued, as fast as possible, and PossibleZeroQ is sometimes very slow. One solution ...
580 views

### How to pick a solution from a list of solutions using a test?

I have a list of solutions that depends on a parameter b3 and I'd like to get the solution for which the x value is minimal when ...
196 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. ...
155 views

### How can I test properties of a symbol without unwanted evaluation

Problem How to get the head, size, dimensions, etc. of a symbol without evaluating it? Since Mathematica does not allocate fix storage space and type to symbols it is not trivial to query runtime ...