## Top new questions this week:

### Does Mathematica have a built-in tool that allows one to operate on both sides of an equation?

Geogebra has a very neat CAS view that allows one to solve an equation step by step in the following fashion: $\quad \quad \quad \quad \quad \quad \quad \quad \quad$ You type an equation and ...

equation-solving

### Solve a trig equation system

Background of the problem In the same plane, P is a fixed point, A,B,C are moving point, PA=a, PB=b, PC=c, find the maximize perimeter of △ABC. let ∠BPC=A, ∠CPA=B, ∠APB=2*Pi-A-B, then the ...

equation-solving performance-tuning symbolic geometry

### my Mathematica has turned orange and not able to find out why

I do not know what happened. But when I rebooted my PC, now Mathematica comes up orange colored. I shut down the PC and tried again, it is still orange. Here is screen shot: I also did a reset. ...

notebooks

### How to retrieve current FaceForm?

The current colour in a Graphics object can be retrieved using CurrentValue["Color"] for use in Dynamic stuff. Example: Graphics[ {RGBColor[2/3, 1/3, 2/3], Dynamic[{If[CurrentValue["MouseOver"], ...

graphics dynamic undocumented style

### Using Simplify on a consistent system returns False

Bug introduced in 8.0 and persisting through 10.1.0 or later It's late, but am I missing something here? Why should two independent equations, which together are consistent, Simplify to False? ...

equation-solving bugs simplifying-expressions

### Modifying strings in a list efficiently

I have a list of strings $\{s_1,s_2,\ldots,s_n\}$. I would like to to produce the following list of strings: $$\{s_1<>1,\ 1<>s_2<>1,\ldots,\ 1<>s_n\}$$ In other words, I want ...

list-manipulation string-manipulation

### Finding self-intersections of a closed curve represented by an interpolation function

I've been trying to find particular simple closed curves on a plane. k = x'[t]*y''[t] - x''[t]*y'[t] + 2 a (y'[t]*x[t] - x'[t]*y[t] - y'[t]*Tanh[2 a*x[t]]); a = 1; curvatureConst = ...

numerics interpolation intersection

## Greatest hits from previous weeks:

### How to make Jacobian automatically in Mathematica

If we have two vectors, a and b, how can I make Jacobian matrix automatically in Mathematica?  a=\left( \begin{array}{c} \text{x1}^3+2\text{x2}^2 \\ 3\text{x1}^4+7\text{x2} \end{array} ...

vector-calculus

### How to find all the local minima/maxima in a range

I want to find : all local maxima in range all local minima in range From those points I can interpolate and combine functions upper and lower boundary. What I am really interested in, is the ...

mathematical-optimization peak-detection

### NMinimize with NIntegrate (crash in symbolic evaluation, memory leak)

This is a "common" problem from what I've seen, but with a different spin. I have a function I use often that finds a fit of an expression to another expression with some free parameters (e.g. for ...

evaluation mathematical-optimization memory

### Why is the Max function so slow when operating on lists of dates?

Example: dates = DateRange[DateObject[], DatePlus[DateObject[], 15]]; First[AbsoluteTiming[Max[dates]]] (* 21.364247 *) As a workaround, DateObject[Max[AbsoluteTime /@ dates]] will get the same ...

performance-tuning