Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

learn more… | top users | synonyms (4)

0
votes
0answers
46 views

How can I eliminate infinite error messages from “Solve” function with multiple linked functions?

I am trying to extract four solutions from four equations which are linked together. I am using the "Solve" function with 4 equations and 4 unknown variables to solve. I have created the function to ...
0
votes
1answer
92 views

How smart is Solve? Figuring out what tricks I should try

I'm trying to solve a large system (~10000) of linear equations using Solve, but the process keeps failing. As-is, I don't know whether it's failing because it's using too much memory or too much time ...
6
votes
4answers
160 views

Combining solutions while solving

Here is a simple representation of my problem. I want to solve Solve[(w^2*c^2 /. #) - 1 == 0, w]& /@ {{c -> 1}, {c -> 2}} ...
0
votes
1answer
54 views

FindMinimum and NMinimize to solve equations

I know that I'm not a Jedi in solving Equations and minimizing functions; but now I've this problem, and the solution is far to me. I want to solve this equation: ...
8
votes
4answers
357 views

Solve symbolically a transcendental trigonometric equation and plot its solutions

I currently have the equation below for a beam with a hinge at various locations, the variable a can vary between 0 and 0.5. $$ Tan\left( {a\sqrt \alpha } \right) + Tan\left\{ {\left( {1 - a} ...
2
votes
2answers
248 views

How can I get this sum? [on hold]

I want to sum the following numbers. At present I am calculating my sum as follows. a = 10^20 + 10^30 + 10^40; In the above case, if I want to add 100 or more ...
1
vote
1answer
82 views

Applying N to the roots found by Solve gives complex numbers when the roots are real [on hold]

I have a function which is f(x) = x^3 - 5 x^2 - x + 1. When I solve for x to find the zeros ...
0
votes
0answers
32 views

Plot solution of NSolve depending on the parameter [on hold]

I would be very grateful if someone could help me with this: I have an equation (which is quite difficult one involving PDFs, CDFs of some distributions etc.). The only way it can be solved is ...
1
vote
0answers
41 views

How to explain NDSolve that functions must be positive only?

I have a simple system of differential equations to solve but both functions should be positive: x[t] > 0 and y[t] > 0 for all t. I was not able to explain NDSolve this fact so it goes x[t] < 0 ...
8
votes
3answers
245 views

Is there a relatively quick way to solve my integer-valued equation?

This is a very simple problem. It can be solved by nested Forloops that exhaustively test every possible case, throwing out all non-solutions. Find all the ...
15
votes
4answers
8k views

Assign the results from a Solve to variable(s)

I understand Mathematica can't assign the results of a Solve to the unknowns because there may be more than 1 solution. How can I assign the 4 values of following result to variables?
1
vote
0answers
48 views

Comparing two ways of fitting systems of ODEs to data

I'd like to ask you if you see any difference between the two following ways of estimating parameters. Given my system of ordinary differential equations that I want to use to find the values of all ...
1
vote
0answers
51 views

Stability region of midpoint method using Solve and RegionPlot

I've been trying to obtain the stability region in the $(\lambda_R, i\lambda_I)$ plane of the midpoint rule $$y_{n+1}= y_{n-1}+2h\dot{y}_n,$$ for the model problem $\dot{y}=\lambda y$. The roots for ...
0
votes
0answers
15 views

Calculate distance base on value that is vary [migrated]

I am new to Mathematica. I am stuck at getting one specific value after calculating with value that is changing from 0.5 to 1.0 I have value 400 and from that I want to go to destination 720 using ...
2
votes
1answer
121 views

How to propel the integration of time a little bit further? Numerical solution can not evolve to the max time

I try to solve a nonlinear partial differential equation. I obtain a numerical solution which can not continue to the max time I set, I always receive message NDSolve::ndcf: Repeated convergence ...
1
vote
1answer
60 views

How to solve this equation?

Mathematica does not give me the correct solution (-1) for this equation: Solve[9^(x + 4) == 27^(1 - x), x] Do I miss something or is Solve the wrong approach ...
0
votes
0answers
49 views

Rearranging 5 equations

I am trying to rearrange 5 equations in terms of 5 variables. I have the equations for y1, y2, ...
0
votes
0answers
34 views

Decompose the functions into partial fraction [on hold]

Decompose the functions into partial fractions f[x] = 2/x^2 - 2 x - 8 How to write partial fractions in Mathematica?
1
vote
1answer
63 views

NSolve for complicated equation involving double cross product

I have the following issue. I am trying to solve a 3-vector equation for the vector slx, sly, and ...
2
votes
1answer
96 views

Double integral changing the limits

This integral does not evaluate: Integrate[ Integrate[1/(E^((a - c)^2 + (b - c)^2) ), {c, 0, 1}], {b, -Infinity, Infinity}] However, reversing the integrals ...
2
votes
0answers
62 views

Solving a system of two nonlinear equations with many symbolic parameters

I have two nonlinear equations with two unknowns, $x$ and $y$, and many symbolic parameters, $a, b, c, d$. They look someting like: $\frac{1}{x}(1+x)^a (1-b)(cx+dy)=0$ ...
2
votes
1answer
99 views

How to figure out whether a nonlinear inequality holds or not

I have an inequality consisted only of seven parameters as follows: $(1 + g)^{-(m+w)}\big[\big\{a+(1-a)(1 + g)^m\big\}(1 + p q)Q - (1 + g)^w \big\{(1 + g)^m (1 + q)-(1-p)q\big\} Q\big] < 0$ ...
6
votes
0answers
97 views

FindRoot kills kernel

Bug introduced in 7.0.1 or earlier. Persists through at least 10.0.1. I'm having problems with FindRoot killing the kernel. In my real application, I want to FindRoot on a black-box function ...
2
votes
1answer
58 views

Find constants in a function? [closed]

Let's say I have a function f[x] with n constants, e.g. f[x] = c1 * x + c2*x^2 + ... + cn *x^n I also have n conditions to find those constants, e.g ...
-1
votes
0answers
50 views

How can I eliminate “Solve::verif: Potential solution” error message from the Solve function?

I am running a Solve function with some determined variables and some updated functions. The variables with double brackets already have their own values, and the variables with single brackets are ...
-2
votes
0answers
47 views

How can I resolve infinite error message from Solve command? [closed]

I am trying to get 4 types of solutions which are x1,x2,x3,x4 from 4 of each equations with iterations. Two variables need to be updated with the the total X value which is X=x1+x2+x3+x4 and these ...
1
vote
0answers
70 views

How can I solve an equation where indexed variables get updated during iteration?

I am trying to solve for a root for a certain equation, but some of the variables in this equation are indexed and get updated during iteration. The code that I am interested in is like the following: ...
0
votes
1answer
53 views

How can I resolve the insufficient memory to complete the computation problem for solving function with iterated variables?

I am trying to solve for a value x in a function where the variables varies with iterations of K. Also, there is one variable called "rvsum" which is updated with a certain formula as well. I have ...
0
votes
2answers
73 views

Replace $z$ with interpolated function and plotting

I start off with this equation $z(x,y) = sin(xy)$. I create an interpolation from $0 < x < 5$ and $0 < y < 5$. I then use this interpolation on a simple function $w(x,y) = x + y + z(x,y)$ ...
4
votes
2answers
314 views

Intersection of Osculating Circle with a Parametric Curve

I have the following Parametric plot Generated from the following: ...
8
votes
2answers
237 views

How can I only draw outer common tangent to two circles?

I have code worked for drawing common tangent lines to two circles(http://en.wikipedia.org/wiki/Tangent_lines_to_circles), now I want to delete the inner common tangent lines, how? ...
4
votes
7answers
702 views

What is the equation to plot a vertical line?

Please help. Trying to find area between three curves, e^-x, x = 2, y = 1. Can't find out how to plot x = 2. Don't want to use ...
0
votes
1answer
131 views

Solving a Trigonometric parameter

I have a similar case as given before : Solving a Trigonometric function with one parameter Let: m = 1; Dx = 100; ν = 0.25; b = 1; and, ...
10
votes
2answers
620 views

Mathematica isn't sure whether a sum of two positives is positive or not

Mathematica is not able to tell whether a summation of two positive expressions is positive or not. Which is very strange. My three symbolic arguments, $x$, $y$, and $z$, are all real numbers bounded ...
-1
votes
1answer
77 views

Is there a change in V10 with Solve and exponents?

I've encountered a strange problem with V10. I can't quite nail it down, but the Solve seems to be unable to solve equations that it could in previous versions. ...
5
votes
2answers
193 views

Counting Real roots

I'm interested on how to count the number of real roots of a random polynomials in an instant, how to put the result in a table and how to plot it in a graph.I generated 1 million random polynomials ...
1
vote
2answers
182 views

How do I feed data points into an equation to solve NUMERICALLY?

I start with this equation and solve it numerically for $z(x,y)$ in the range $1 < x < 5$ and $1 < y < 5$: $$ \frac{3}{xyz} - 2x - 3y - 5z = 0 $$ Then using the data points of $z$ above, ...
0
votes
3answers
97 views

How to manipulate with external data?

I have a .txt file which contains a lot of triples (a, b, c) (one per row) which should be coefficients of my equation ax^2+bx+c=0. I want to include each triple in .nb file and solve each equation. ...
-2
votes
1answer
99 views

How can I produce a list of solutions for a function which is updated with updated variables using for loop?

I need to loop over a set of equations, solving for X and adding the new X value to the old X value at each step. The output I need is a list ...
1
vote
1answer
89 views

How do I link the txt file data sheet to mathematica and extract exact elements that I would like to use in solving for x? [closed]

I am trying to solve for a numerical solution for an equation which contains variables that evolves as index i incrreases. The actual equation that I am using to extract solution for x with an ongoing ...
1
vote
2answers
70 views

Solving a two point boundary problem for a piecewise system of equations

I'm trying to solve a two point boundary value problem with a piecewise system of equations like: ...
2
votes
3answers
83 views

Solve equations within range and plot [duplicate]

Hi I have these pair of equations to solve: $$ 1 - 3 x y = 5 z - 2 x $$ $$ y = 7 x z - \frac{z}{x} $$ I want to eliminate $z$ and plot $y(x)$ within the range $-2 < x < 2$ and $-2 < y ...
1
vote
1answer
94 views

NDSolve fails for certain choices of parameters and solve range

I'm trying to solve a pair of coupled ODEs with NDSolve. I know roughly what the solution should look like (both should give periodic functions, pi/2 out of phase, the amplitude of which damp towards ...
0
votes
1answer
67 views

Solving a linear system in three unknowns [duplicate]

solve[{2 x + ay - z, bx - 4 y + z, -x + y} == {10, -30, 20}] $$ \begin{array}{lcr} 2x + a\,y - z & = & 10 \\ b\,x -4y + z & = &-30 \\ -x + y & = & 20 \end{array} $$ ...
-1
votes
0answers
55 views

NSolve transcendental equations

NSolve[{Cos[al] == R/(0.0496045\[VeryThinSpace]+ R), Cos[al + 0.1/R] == R/(0.05\[VeryThinSpace]+ R)}, {al, R},Reals] It is not solving, something missing here.
0
votes
2answers
165 views

How to get a solution for the following equation?

When I try to solve this equation using Mathematica: Solve[Exp[b*x]-c*(x^2)-a*x-1 == 0, x] /. {a -> 6.336, b -> 8, c -> 32} I don't get any result and ...
2
votes
2answers
146 views

How to obtain a function from a implicit equation?

I have (60 - r/2) (70 - ca - r/2) - (60 - r/2 - ca + (4/25) (70 - r/2 - ca))*(70 - r/2)==0 Reduce[%, {ca}] But How could I obtain directly a function as ca[r_] ...
0
votes
1answer
134 views

Finding solutions of polynomials system

Let $f_1,...,f_n$ be a set of polynomials in $x_1,...,x_n$ with rational coefficients. I need to check whether a system $$f_1=a_1,...,f_n=a_n$$ has a real solution for large enough count of points. ...
0
votes
0answers
19 views

System of Nonlinear equations with Gamma and Incomplete Gamma function

The next two nonlinear equations are cumulative ratios of a production system. The mathematical model includes two essential parameters (n, tau) that can be obtained by solving this system. I'm ...