Linked Questions

2
votes
2answers
2k views

Rewriting one expression using a variable representing another expression [duplicate]

I have two expressions: w1 = (a+b)/c^2; w2 = (a^3 + 3 a^2 b + 3 a b^2 + b^3)/c^6; How can I ask Mathematica to try to find an alternative expression for ...
0
votes
1answer
3k views

How to write a variable in terms of the other [duplicate]

I have an equation that defines a variable like y=4x+a. I had another equation, z=x+2+4, I would like to know if there is a way in Mathematica to get an expression in which z= a*y+C, in which a and C ...
2
votes
2answers
224 views

Rewriting the set of equations in terms of new variables, using replacement rules when the expression contains partial derivatives [duplicate]

I am working with cumbersome equations, that contain a lot of terms. Here I will consider simple example: ...
3
votes
2answers
120 views

How can I use ReplaceRepeated (//.) in this case? [duplicate]

Consider the following case: (a^3*b) //. {a^2 -> c, a*b -> d} instead of c d the output is: ...
2
votes
1answer
245 views

How can I simplify the result of a differential equation by using my own defined expressions? [duplicate]

I want to solve the following differential equation with mathematica: α β * w''''''[ξ] + ( 1 + α - p ) * w''''[ξ] + p/β * w''[ξ] = 0 The answer seems at ...
0
votes
2answers
235 views

Replacing a expression in another expression with a Variable [duplicate]

I want to set a symbol (or variable) for an expression. Here is an example: A x^2 + C x + D I want to reduce this expression to ...
1
vote
2answers
96 views

How do I format expressions so that replacement rules correctly apply to exponents? [duplicate]

I have a series of rules that I would like to apply to a series of expressions with variables, but cannot get Mathematica to correctly recognize that these rules should apply when my variables have ...
1
vote
1answer
80 views

Solving for a constant multiplier of a variable [duplicate]

I would like to make this manipulation: Solve[r Sin[α[t]] + l Cos[ϕ[t]] Sin[γ[t]] == 0, l*Cos[ϕ[t]]] But it seems that the ...
1
vote
0answers
88 views

Introducing new variables implicitly [duplicate]

I have a calculation expr111 = cs[giso, xiso, 1, 1, 1] that gives the result -((k x)/(2 (1 + 1/4 k (x^2 + y^2 + z^2)))) I ...
0
votes
0answers
62 views

Simplify symbolic expression in terms of constants [duplicate]

Say I have an expression $a+b+a\times b$ and I define $c:= a\times b$. How do I get Mathematica to write $a+b+a\times b$ in terms of $c$, i.e. $a+b+c$?
0
votes
1answer
40 views

Substitution inside an expression [duplicate]

I'm trying to get mathematica to replace an expression with a reduced form. I wanted to replace $(k/w)$ with $h$ in a particular expression, and I've tried something like: ...
0
votes
1answer
45 views

Reducing Output length by introducing new variables [duplicate]

I have outputs like "expression/(1+3*c^2) +anotherexpression/(1+3*c^2)" and so on. Is there any way to set 1/(1+3*c^2)=A where A is a new variable so that the output reads like "A*expression+A*...
1
vote
0answers
34 views

replacement rules don't account for signs [duplicate]

I would like to make a single replacement rule that disregards the sign. I have the following expression: ...
27
votes
6answers
13k views

Replacing composite variables by a single variable

To replace a single variable by another variable, one can simply use the the replace all (/.) operator (e.g., ...
17
votes
7answers
11k views

How do I replace a variable in a polynomial?

How do I substitue z^2->x in the following polynomial z^4+z^2+4? z^4+z^2+4 /. z^2->x ...

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