# Are Mjaavatten

Retired physicist with background in the petroleum and process industry. My main interests are mathematical modelling, numerical methods, and thermodynamics.

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**Content Feed**

Error in setdiff function

One workaround is to replace all NaNs with some spceific value that is not present in your data, say -9999: >> S1 = [1,2,3,NaN,...

19 days ago | 0

How can I solve an ode where one of the variables is a matrix?

A(t) should be a function, not a vector. Below I define A as an anonymous function. I also use an anonymous function for your ...

19 days ago | 0

| accepted

4D data /Index exceed array bounds

I think it may be better to let M_Val be a cell array of 5 ordinary arrays, where M_Val{k} is of dimension 134 by 2 by nsyll(k)....

20 days ago | 0

4D data /Index exceed array bounds

I think you may have inadvertently created a cell array containing your whole data matrix in element 1. Something like this: >...

21 days ago | 0

How to find index range of range of values in an array

i = find(x>=69 & x<=72);;

4 months ago | 1

y coordinates of center of buoyancy

Is this what you want? x = [-8,-8,-6,0,6,8,8,-8]; y = [10,5,1,0,1,5,10,10]; ship=polyshape(x,y); figure(1) clf hold on p...

4 months ago | 0

Is it possible to convert a cell array into individual variables on workspace?

Dynamically creating variables in Matlab is not encouraged. See Stephen Cobeldick's tutorial entry. A better idea is to create ...

5 months ago | 0

How to plot a trinomial graph

fun = @(x) x^3; fplot(fun,[-3,3]) Alternatively: x = linspace(-3,3); plot(x,x.^3); % Note the use of .^, for element by ele...

5 months ago | 0

Fitting a 3D gaussian to a 3D matrix

meshgrid arranges the xx and yy output matrices to fit the convention where the surface plots have x on the horizontal axis and ...

6 months ago | 0

For loop assistance- incorrect data

You give DATA.s(3,1) the desired value in line 8 of exec2w. Then you overwrite it with the wrong value in line 22. I found deb...

8 months ago | 0

How can resolve r0<=r0_max?

I interpret your question to mean that you want copertura{mm,nn}(k,1) to take the value 1 if r0{mm,nn}(k,1) <= r0_max(mm,nn), an...

9 months ago | 0

Increasing precision of second order boundary value problem

Your asymptotic expansion solution seems to have zero slope at y = 0. This implies that the second derivative is zero and the s...

12 months ago | 0

Error using + Matrix dimensions must agree.

In line 43, x(:,i) is a column vector, while k1' is a row vector. Summing a column vector and a row vector is not allowed in ol...

1 year ago | 0

Golden Section Search algorithm, golden number why is 0.381

Let and be the end points of the current range. In golden ratio search we choose a new point such that the ratio of the two ...

1 year ago | 1

Problem relating to mathematical expression

Ameer's answer is correct, of course. Here is another approach, without the elegant Matlab functions: N = 5; % Max window size...

1 year ago | 0

Help text does not work for user-defined functions

Problem solved - finally! My Matlab 2019b and 2020a installations had several other odd behaviours in addition to the help prob...

1 year ago | 3

| accepted

Solution for system of two non linear equation

You can rewrite you equations as (Nd-x-y)-a*(x*(x+y)) = 0 (Nd-x-y)*(No-y)-b*(y*(x-y)) = 0 where x = Nd, y = Nonegative, a = ...

1 year ago | 1

| accepted

Problem of erf when using fmincon

Your problem has infinitely many solutions. Whenver x(1)-x(3) = 1 and x(2)-x(4) = 1, fun = 0, which is the minimum value possib...

1 year ago | 0

how to Nonlinear equations?(two variables)

Although R1 and R2 are nonlinear finctions of t, your equations are linear in x. So you write the equations on the form A(t)*...

1 year ago | 2

| accepted

How to count number of times a number appears in column B based on column A

letters = 'ABAACD'; numbers = [1,2,2,1,1,3]; uniqueletters = unique(letters); uniquenumbers = unique(numbers); n = length(un...

1 year ago | 0

| accepted

Van der Waals equation - Newton's method

In your code, newton_ndim does not know the value of T and so cannot call fun(X,T). You can probably fix this by defining an in...

1 year ago | 0

| accepted

How do I solve system of equations?

If I understand you correctly, your system consist of 128 eqations. a and b are arrays of 64 unknowns each. You must then solv...

1 year ago | 0

| accepted

Join repeated continuous elements of a vector

in = [1 1 1 2 2 3 6 6 6 1 1 1 4 4 4 2 2 2 6 4 4]; i = 1; count = 1; out = []; a = in(1); while i < length(in) i = i+1; ...

1 year ago | 0

Fsolve don't work good with trigonometric

Your function has several different zeros. Which one fsolve finds will depend on the starting point. I ran: f = 100; while no...

1 year ago | 0

Question

Help text does not work for user-defined functions

I just installed R2019b and the help function does not work. Example: I created the addme function from the Add Help for Your P...

1 year ago | 2 answers | 2

### 2

answersQuestion

Is there a way to avoid repeating time-consuming calculations from odefun in the events function?

The right-hand side in my ODE is quite time-consuming. In the course of calculating dy/dt I calculate a variable u that I also u...

2 years ago | 2 answers | 0

### 2

answersFirst order ODE parameter fit to dataset

The challenge is how to use your table of temperatures in your updateStates function. At a given time t, you must interpolate y...

2 years ago | 0

| accepted

How to calculate a curve for different variables?

Here is one way to do it. I have reduced the number of elements in your Time and V vectors in order to make a nicer surface plo...

2 years ago | 0

| accepted

datetime default stetings 12/24

Use HH instead of hh for the hours: >> datetime.setDefaultFormats('default','hh:mm:ss yyyy-MM-dd') >> t = datetime(2019,8,10,...

2 years ago | 4

| accepted

How to read a file containing non numerical characters and commas?

The 22 lines of text are easily dealt with using the 'HeaderLines' option. Next you must convert your strings to doubles. Below...

2 years ago | 0

| accepted