# Tagged Questions

How to manipulate expressions structurally, not necessarily complying with the rules of algebra.

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### How do I use Replace All? [duplicate]

I have an expression: a + b 2^(1/2) + (c + d 2^(1/2))*I I want to replace each occurrence of 2^(1/2) with ...
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### How to organize expression by symbols (like Collect), but apply different functions to each coefficient

I want to mimic the functionality of Collect[expr, {vars}, func], but with the following modification: The function f that is ...
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### Replace function and its derivatives [duplicate]

When I have a complicated expression that depends on some variable, say, $f$, the following usually works ok: Expression ./ { f-> x^2 } But if $f$ is a ...
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### Solving a trigonometric equation for all $x$ using constant coefficients

I want to find the coefficients $a$, $b$, $c$, etc. that make an equation like $a+bx=x$ true for all $x$, but for trigonometric functions of $x$. For example ...
96 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 ...
50 views

### Misunderstanding of Replace code

I am looking for the right way to replace $\delta \, \, \text{by} \, \, 0.05 \, \, \, \beta \, \, \, \text{by} \, \, \, 1.77 \, \, \, \text{and} \, \, \, n \, \, \, \text{by} \, \, \, 12$ in this ...
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### How to update values of nested association using AssociateTo?

Saying we have an association: asc = <|"A" -> <|"a" -> 1, "b" -> 2, "c" -> 3|>|>; I want to updated values of ...
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### How can I prevent exponents from appearing in an expression?

I've found posts dealing with showing/hiding exponents for numbers, like in scientific notation. But what if I have a general expression? I have an expression like this, ...
36 views

### Factoring rationals from equation based on digit complexity?

Consider an equation of the following type: ( poly = (3 x)/35 + (6 y)/7 ) == 0 If we apply the command Factor to this ...
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### How to label outputs from Print [closed]

I have problem with Print in Mathematica. The data that I get from it, is not labelled so that I can use it elsewhere, therefore I have got to label them manually. ...
82 views

### Extract coefficients from trigonometric polynomial [closed]

Suppose I have: f[r_, ϕ_] = C1 Cos[ϕ]r + C3 Sin[3 ϕ] r + C4 Sin[4 ϕ] r^4; How do I extract the coefficient of a chosen trigonometric term, let's say ...
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### Extracting factors from an expression

I want to transform expressions into lists of elements. For example, b*c + a*b*c /. Plus -> List /. Times -> List ...
86 views

### Separate integer fractions from variables?

Whenever I write a rational number times a variable, i.e.: (2/3)a the result Mathematica displays looks very cringeworthy: $$\frac{2a}{3}$$ I would prefer ...
106 views

### When is the righthand side of a RuleDelayed evaluated?

The documentation on RuleDelayed states that lhs :> rhs represents a rule that transforms lhs to rhs, evaluating rhs only after the rule is used. Consider the following rule: ...
512 views

### How to replace the first Head of a currying expression like “a” in a[b,c][d]?

How do we replace the first Head of a currying expression such as a[b,c][d]? When accessing the ...
82 views

### The role of comma in the syntax of Part

I can't understand the syntax of Part, namely what does , do. The documentation says that ...
55 views

### Replacing product of functions wih another function

I have a function which depends on w,x,y,z. Let me call ...
86 views

### ToExpression to Latex Parenthesis

Everytime I use ToExpression to transform a TeX expression into mathematica input form, Mathematica always interprets parenthesis ('(' and ')') as square brackets, ...
45 views

### Prevent Plus from reordering terms by default? [duplicate]

Writing Plus[a,b]//FullForm gives back Plus[a,b], while Plus[b,a]//FullForm again returns <...
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### ToExpression processing errors

Is their a way to get a more comprehensive return value when running ToExpression? For example when I run ...
147 views

### Select largest number using pattern

I have the following expression: myExpr=R[C[2],B].(II+R[C[3],C[2]].(II+R[C[4],C[3]])) I need to create a pattern which would replace the ...
107 views

### Converting an expression to function [duplicate]

I have the following problem. I current can automatically create the variable positionPayload, for instance: ...
81 views

### Derivative of vector dot product with respect to a vector

I have the expression: Transpose[gvecI, {2, 1}].x (m[1] + m[2]) gvecI and x are [3x1] ...
118 views

### Simplifying Expressions for FindMinimum

I am currently trying to apply the FindMinimum function to find the lowest energy of an expression. My current expression as of now is relatively complicated. It is the summation of 48 similar terms, ...
56 views

### Position not working? [closed]

I have the list: myList={0,0,0,a,b,c,0,0,d} I need to find the positions of all elements that are non-zero. I do like this: ...
82 views

### Find sub-sets of vanishing additions or subtractions from a list?

Let's say I have a list L containing n numerical numbers. Now I want to find all sub-sets of ...
67 views

### Dropping rational coefficients

I have a list of expressions (they all are exact numeric quantities, not containing any variables), some of them have integer or rationals coefficients, or complex coefficients with rational or ...