# Are Mjaavatten

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

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**Feeds**

Difficulty Finding Hydrogen (H2) Properties for Gas Properties (G) Block

The real gas option in Simscape requires tables of properties as functions of temperature and pressure. You will find the data ...

1 year ago | 3

| accepted

Question

How do I create a table containing a character array if it has only one row?

This works fine: Time = [1;2];Force = [12;17];ID = ['ab';'cd']; T = table(Time,Force,ID) But this fails: Time = [1];Force = ...

2 years ago | 1 answer | 0

### 1

answerError 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,...

3 years 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 ...

3 years 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)....

3 years 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: >...

3 years ago | 0

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

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

3 years 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...

3 years 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 ...

3 years 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...

3 years 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 ...

3 years 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...

4 years 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...

4 years 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...

4 years 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...

4 years 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 ...

4 years 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...

4 years 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...

4 years 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 = ...

4 years 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...

4 years 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)*...

4 years 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...

4 years 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...

4 years 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...

4 years 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; ...

4 years 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...

4 years 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...

4 years 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...

5 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...

5 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...

5 years ago | 0

| accepted