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# Josh Meyer

Last seen: 7 days ago Active since 2013

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List of built-in data sets, please
In R2021b, there is now a documentation page with a selection of useful data sets that are in MATLAB: MATLAB Example Data Sets

9 months ago | 3

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Filtration modelisation pdepe derivation problem
Is phi supposed to be a function of x? You currently have phi=linspace(0,0.7,100); and xmesh=linspace(0,0.5e-6,50); So, ...

1 year ago | 0

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Can pdepe be used when there is a boundary condition in the centre of the system - Invasion assay
This example shows how to solve a system where there is a material interface: https://www.mathworks.com/help/matlab/math/solve-...

1 year ago | 0

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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) ...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 0

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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 ...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 0

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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...

2 years ago | 1

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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...

3 years ago | 0

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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...

3 years ago | 0

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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...

3 years ago | 0

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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...

3 years ago | 0

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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 ...

3 years ago | 0

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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 ...

3 years ago | 0

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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. ...

3 years ago | 0

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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...

3 years ago | 0

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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....

3 years ago | 0

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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...

3 years ago | 1

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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 ...

3 years ago | 3

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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...

3 years ago | 1

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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 ...

3 years ago | 0

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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...

3 years ago | 2

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'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 ...

4 years ago | 0

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Use griddata ignoring gaps in data
To interpolate without the gaps you need to remove them from the data before interpolating, request values on the full grid (inc...

4 years ago | 1

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system of 1st and 2nd order differential equations ode45
The documentation explains how to express higher-order equations as first-order equations: <https://www.mathworks.com/help/matl...

4 years ago | 0