Community Profile

# Josh Meyer

### MathWorks

139 total contributions since 2013

I write MATLAB Math documentation

View details...

Contributions in
View by

ODE System with 4 equations
When you have a system of equations, each equation gets its own spot in the solution vector y. With the conventions y(1) ...

3 months ago | 0

| accepted

How would I manipulate the following functions to use a tall array?
First you need to make a datastore that references the underlying files for each array (one datastore per array). Then you can c...

4 months ago | 0

possibility to add a timeror on ODE15s which after a certain time limit, the solver is stopped or gives a null output
You could implement an event function to do that: https://www.mathworks.com/help/matlab/math/ode-event-location.html Use start...

4 months ago | 0

Solve heat problem by using pdepe
Assuming you want to enforce pr = ur+20; at t=0.03, then you can split the problem into two sub-problems that are solved separat...

5 months ago | 0

Where can I get a samaritan to help me with my code of a Reaction–Diffusion Delayed Neural Networks
You should be able to use pdepe. Just calculate tau in the pdefun function and pass the delayed time value when you call the sub...

6 months ago | 0

Boundary conditions for a ring PDE
pdepe does not allow for time derivatives in the boundary conditions. The boundary conditions are expressed in terms of the flux...

6 months ago | 0

how i can solve the following PDE using periodic boundry coditions
Periodic boundary conditions require that when something leaves one boundary with a certain velocity, it enters the boundary on ...

6 months ago | 0

| accepted

PDEPE: How to set I.C as a variable?
pdepe has expectations for the initial condition function. Namely, that it will use the functional signature: function u0 = icf...

6 months ago | 0

Writing PDE boundary conditions
pdepe expects the boundary conditions to be written in a standardized form: Notice that only p can depend on the variable bei...

6 months ago | 0

What is the “pdentrp” function in the “pdepe” function?
This is an internal, private helper function, so it does not have documentation beyond help text. You can access the file with t...

6 months ago | 1

Retaining the max value during scattered data interpolation
You'll need to do this manually before calling scatteredInterpolant. There are a few ways to do it, you could use a logical mask...

11 months ago | 0

| accepted

PCG and MINRES question
Since A*x = b, the sizes of the variables must be: A * x = b (M-by-N) * (N-by-1) = (M-by-1) But since alm...

11 months ago | 0

Getting the intermediate solutions in an iterative solver
While the functions themselves don't return intermediate results, consider that the resvec output of all the iterative solvers r...

11 months ago | 0

why convergence is not happening in pcg function ?
There are two things to notice here: In the first message you printed where PCG converges after 1 iteration, this is an indicat...

11 months ago | 0

PCG on a large sparse matrix from Finite difference method
Yes, you can provide the coefficient matrix as a function handle instead of a numeric matrix. This is because PCG, like many of ...

11 months ago | 0

Best integration method to integrate this oscilating function
integral can handle oscillatory integrands as long as there aren't too many oscillations, and you supply plenty of WayPoints in ...

1 year ago | 0

Processing Data in a Tall Array
findgroups and splitapply work with tall arrays, so don't worry about using tall.transform or tall.reduce for this simple task. ...

1 year ago | 0

How does integral2 work?
The basic principle of numeric integration is you are calculating the area under the curve by splitting it up into smaller piece...

1 year ago | 0

| accepted

Problem with boundary conditions for PDEPE
From the doc for pdepe, "When m > 0 and a = 0, boundedness of the solution near x = 0 requires that the flux f vanish at a = 0....

1 year ago | 0

| accepted

what's the difference in accuracy between solving a stiff problem by ode15s and ode45?
Stiffness is more of an issue of stability than accuracy. Nonstiff solvers can solve stiff problems, it just takes them a long t...

1 year ago | 1

Change font size of node name in a graph
Several new properties were added to GraphPlot objects in R2018b to enable customization of node and edge labels. In particular ...

1 year ago | 2

| accepted

Problems with pdepe with disconnected variables in c, f and s
c, f, and s are expected to be column vectors with length equal to the number of equations being solved. Since you have 1 equati...

1 year ago | 1

| accepted

Implementing boundary condition in pdepe
The form for the boundary conditions expected by the solver is Since you have a system of two equations, each p and q should ...

1 year ago | 0

pdepe help! (boundry condition in PDE solver)
Your boundary condition function includes the line pl = ul-TT(i); TT(i) is not defined within view of the function, so that i...

1 year ago | 1

| accepted

Submitted

Plotting the Binomial Coefficient
Live script that plots the binomial coefficient over all positive and negative argument combos.

Solved

Project Euler: Problem 2, Sum of even Fibonacci
Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 te...

2 years ago

Solved

Triangle sequence
A sequence of triangles is constructed in the following way: 1) the first triangle is Pythagoras' 3-4-5 triangle 2) the s...

2 years ago

Solved

Find a Pythagorean triple
Given four different positive numbers, a, b, c and d, provided in increasing order: a < b < c < d, find if any three of them com...

2 years ago

'Undefined Function or Variable' Error when Function is Defined
Looks like the issue is you define cp in the workspace and the function can't access that variable when it gets called. So, try ...

3 years ago | 0

| accepted