Questions tagged [semantic-matching]
Posts about semantic pattern matching rather than syntactic pattern matching (which is the built-in pattern matcher of Mathematica) e.g. "Why x^3 /. x^2->a doesn't work!"
27 questions
1
vote
3
answers
162
views
How to keep a specific expression unevaluated?
For example, I define some quantities here
$$
\gamma=\frac1{\sqrt{1-\frac{r^2}{c^2 t^2}}}, \qquad \mbox{with} \; r^2=x^2+y^2+z^2.
$$
Now I want to calculate some expressions. Let's say, $\partial_t \...
- 409
2
votes
2
answers
122
views
Ask Mathematica to prioritize writing an expression in terms of another
I have an old reference text with tables of solid spherical harmonics expressed in cartesian coordinates. (Edit: Here's a digital version of said table, for the curious.) In an attempt to replicate ...
- 123
3
votes
5
answers
190
views
Importing Specific Data from a Text File
I am quite new to Mathematica. I have a text file that upon importing has a repetitive structure with characters included. I need to extract only the following in numbers only (no letters, dash lines, ...
- 33
3
votes
2
answers
47
views
Trouble with replacement rules for squared variables [duplicate]
I want to do replacement of products (because I am dealing with abstract projectors), but Mathematica seems to fail understanding this toy example replacement :
...
- 375
5
votes
1
answer
214
views
How to Replace 'delta t' with 'a' in Mathematica Without Affecting Separate Instances of 'delta' or 't'?
In Mathematica, how can I replace instances of delta t in an expression with a, while keeping instances of ...
- 215
0
votes
3
answers
59
views
How to replace polynomials numerically? [duplicate]
We know that the value of this equation is 0
x2 y1 - x1 y2 == 0
For the following equation, there is a correlation between the polynomial parts of the known ...
- 1
1
vote
1
answer
115
views
Expression substitution
I konw:
$$
a_0=\frac{4 \pi \epsilon_0 \hbar^2}{m_e e^2}
$$
and
$$
\alpha = \frac{m_{\mathrm{e}}^2 e^4}{18 \pi^3 \epsilon_0^2 \hbar^4}
$$
So we can use $a_0$ for $\alpha$,like this:
$$
\alpha=\frac{m_{\...
- 1,630
0
votes
0
answers
76
views
Neural network: Segmentation of water and not water area
Good morning everyone. I have a large dataset of photographs similar to the one attached. It would be my intention to train a neural network to recognise water and "non-water" zones. How ...
- 109
4
votes
4
answers
193
views
How to use replacement rules in a named expression before a sub-expression evaluates?
I have a named expression: expr := a + b. a and b are also named expressions.
Let's say <...
2
votes
1
answer
182
views
How to replace Divide in an expression?
It seems that a/b is always replaced with the form: a * b^-1, Times[a, Power[b, -1]]. I ...
4
votes
3
answers
205
views
Rule can not work? [duplicate]
For example I have this equation,I want to use c->a/b ,but it can not work
$$
\frac{a^2}{b^2}+\frac{b^2}{a^2}+\frac{a}{b}+e^{a/b}+\frac{b}{a}+\log \left(\frac{a}{b}\right)
$$
...
- 1,630
2
votes
2
answers
139
views
How can I change variables, if the variables I want to change to are not directly stated in the term?
So I don't mean something like this
f[x_] = x^2
f[x] /. x^2 -> y
But what I mean is something like this:
where the variables I want to change to are defined ...
- 177
5
votes
2
answers
278
views
What is a nice way to convince Mathematica to use $\tau$ instead of $\pi$ in evaluated formulas?
I have tried like
Replace[something, {2*π -> HoldForm[τ]}]
Although it works well where a lone 2 π symbol, it fails to ...
- 153
3
votes
1
answer
201
views
ReplaceAll with Powers [duplicate]
If I run the following code:
a^2/b^2 /. {a/b -> c}
I'm getting output:
a^2/b^2
How can I obtain ...
- 33
2
votes
0
answers
247
views
What is Wolfram's equivalent of Maple's algsubs?
Maple has two primary substitution functions.
subs - which is similar to ReplaceAll in WL.
algsubs - which does replacement but takes into account the algebraic ...
- 9,751
2
votes
2
answers
372
views
How do you get substitution to recognize a derivative?
I have a simple expression involving a derivative:
x[t_] = Q/T[t];
Simplify[Derivative[1][x][t] /. Q -> x T[t]]
That produces:$$-\frac{x T'[t]}{T[t]}$$I have ...
- 1,610
5
votes
3
answers
752
views
ReplaceAll (/.) not working as expected
I am trying to replace some variables in the form of n*wt with wt. However, I came across some cases where the ...
- 1,327
4
votes
2
answers
337
views
Definition of a general rule
By defining:
rule = Sqrt[expr_^2] :> expr;
and writing:
Sqrt[x^2] /. rule
I get:
x
which is what is desired (...
- 4,462
0
votes
1
answer
43
views
Parsing time interval strings as "Uncertain" Time Intervals
Problem: I have strings of form "[d1, d2]" or sometimes just [d1] where d1 and ...
- 3,175
9
votes
1
answer
1k
views
How to find multi-word synonyms?
I’m looking to write a semantic distance function for phrases (5 words or less) that can map multi-word synonyms together. My domain is e-commerce fashion - here are some required examples for a ...
- 31.8k
0
votes
1
answer
200
views
Using Semantic Import to do an Excel-like VLookUp using Mathematica
I'm following an example provided in the following
Stack Exchange Link
but, using a different approach. My data is contained in an Excel workbook called "Input Workbook.xlsx"
as shown here:
I ...
6
votes
2
answers
420
views
"Smart" substitution of subexpressions
I have the following question.
An expression, which I want to simplify contains several subexpressions which appear quite frequently all over the place. To optimize simplification I would like to ...
- 245
3
votes
0
answers
142
views
SemanticImport extremely slow with "Number" format
With the following definition:
col = "num\n" <> StringRiffle[Table[i, {i, 1000}], "\n"];
I do not understand why the ...
- 1,225
2
votes
2
answers
234
views
Sets of identical equality/inequalities
So I've used Mathematica for some months, but I never noticed this sort of thing about it, namely:
(a > b) == (b < a)
which are supposed to be identical ...
- 283
0
votes
1
answer
195
views
4
votes
4
answers
850
views
How to apply ReplaceAll to denominator?
Here is the simple task. In reality, it's far more complicated, but it comes down to this.
I want to take the expression $\frac{y}{x^2}$ and replace $x^2$ with $k$. This doesn't work:
...
- 133
60
votes
4
answers
11k
views
Can I simplify an expression into form which uses my own definitions?
This seems like a simple thing to do, but I couldn't find anything relevant from Mathematica documentation.
So suppose I have an expression:
a*b/(a + a*Cos[a/b])
...
- 981