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Rafael Hernandez-Walls


Last seen: 27 days ago Active since 2010

My interest is everything related to numerical schemes applied to PDE and Oceanography, UABC.

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Answered
Determine if any key is being pressed
If only use the function: pause

1 year ago | 0

Answered
matlab not plotting graph
You need one point in the equation of z h = [2,4,6,8,10]; x = 10.1; y = 2.5; z = (x * h.^2 - x - sqrt(y^2*h.^2 - y^2))./ (h....

1 year ago | 0

Answered
how i can find the chessboard lines and draw on the main image with any solution
Maybe you can use the Radon Transform, like this link: https://www.mathworks.com/help/images/detect-lines-using-the-radon-trans...

1 year ago | 0

Answered
how can I get y which correspond to x and then plot (x,y)??
Try this: x=linspace(-4,4); for r=1:length(x) y(r)=fzero(@(y)y.^3+0.2*exp(-1*x(r).^2)*y.^2-2.2039*y.^2+0.8155,1); end p...

1 year ago | 0

Answered
How to read data from text file and store as it is with variables
Assuming you have a file with only following line (name of file= 'algo.txt'): phi1_32_1 = 1 You could then read the line with...

1 year ago | 0

Answered
numerical simulation of travelling wave of epidemic model
try this.... clear all; xl=0; xr=1; %domain[xl,xr] J=1000; % J: number of dividion for x dx=(x...

1 year ago | 0

Answered
Read a txt file
try this Dens1 = [A(:,1),9.11*A(:,2).^(1.326)]; fileID1=fopen('E1.txt','w'); % [n,~]=size(Dens1); for k=1:n b=fprintf(...

1 year ago | 0

Answered
How to display correlation coefficents on plot?
you can try something like this: x = [0 0.000009 0.000018 0.000028 0.000037 0.000046 0.000055 0.000065 0.000074 0.000083 0.0000...

1 year ago | 0

Answered
extracting value from a matrix
I think it is better to put the variable X as a string and from there start. for example: X=['1000000000000000000000000000000...

1 year ago | 0

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Answered
How to get Taylor polynomial for functions?
You can use a function that is in the MAThWORKS fileexchange (I put the link): str=input('Function? ','s'); %tray with: cos(x)...

1 year ago | 0

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Answered
Change the sign of a Vector over N intervals
Use something like this: Y=rand(1,20); d=[1:4,8:12,17:20]; Y(d)=-Y(d)

1 year ago | 0

Answered
For loop only outputting the final value.
Try using something like this: t=linspace(0,3*pi,100) t=linspace(0,3*pi,100); for k=1:length(t) y = q2(t(k)); val...

1 year ago | 0

Answered
Plotting log x and y
Why don't you treat like this: n = 30; x = 0.5; h(1) = 1; emin = 1; for i =1:n if i==1 h(1)=0.5; else ...

2 years ago | 0

Answered
How can i draw the graph of this two functions using matlab
when i have this like problem i use this code: t=linspace(0,2*pi,50); f=((t>0)&(t<=1)).*2+((t>1)&(t<=pi/2)).*0.5.*t.^2+((t>pi...

2 years ago | 0

Answered
Finding the length of square function
t2=t(find(diff(X)>0)); t1=t(find(diff(X)<0)); long_time=t2(2)-t1(2)

2 years ago | 0

Answered
How to create a sine wave with variable frequency - Simulink
something like this: (?) t=linspace(0,2*pi,100); f=rand(1,100); y=sin(f.*t); plot(t,y)

2 years ago | 0

Answered
Euler method returning error
maybe you need copy the function eulsys.m in your system. In this link you have a copy: http://macs.citadel.edu/chenm/344.dir/0...

2 years ago | 0

Answered
how do i plot only certain part of cepstrum
KSSV ks suggests that you work with the index, here I show you an example of what KSSV mentions, x=linspace(0,10,100); y=x.^2;...

2 years ago | 0

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Answered
creating multiple values of the same x,y,z
x=[ 2, 4, 2]; repmat(x,10,1)

2 years ago | 0

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Answered
no data plots on graph (plot (x,y))
David is correct. Why don't you try something like that in your code... d(1) = 32000; H = 8000; Re = 6370000; %c2 = 0.5*exp(...

2 years ago | 0

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Answered
Invalid syntax error with a simple code
tray this x = [-2 -1.5 -1 -0.5 0 0.5 1 1.5 2]; y = (x+x.*(sqrt(x+3))).*(1+2*(x.^(2)));

2 years ago | 0

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Answered
How can I obtain slope of a trend line calculated for a time serie
Maybe this is useful for you https://www.mathworks.com/help/matlab/ref/detrend.html

2 years ago | 0

Answered
Why does my plot not appear?
Vmax = 354*10^(-6); Km = 1.5*10^(-3); S = .0000005:.0000005:.000030; v = Vmax*S./(Km + S); plot(S,v);

2 years ago | 0

Answered
Multiple Iterations over a system of linear equations
I think the problem is where the plot function, maybe you need to put another command to plot in each iteration, something like ...

2 years ago | 0

Answered
for loop and if-statement
This may help you Time=[0.5 1.51 2.6 3.65 4.71 6.8 7.9 9.1 10.3 11.1 12.3 15 16.2 17.3 18.5 19.6]; dife=diff(Time); heelstrik...

2 years ago | 0

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Answered
"Z must be a matrix, not a scalar or vector." PLEASE HELP!
x1 = 1:.1:4; x2 = 1:.1:4; [X,Y] = meshgrid(x1,x2); Z= ps2func(X,Y); mesh(X,Y,Z) grid on hold on function [f]=ps2func(x...

2 years ago | 1

Answered
Converting Euler's method calculation into matlab
tray this: % Initial conditions and setup Q=400; A=1200; alph=160; h = 0.5; % step size t = 0:0.5:10; % the range of t ...

2 years ago | 1

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Answered
Lotka-Volterra Predatir Prey Model Code
using this: function [dPdt] = lotkavolterra(t,P) alpha = 1.5; % you have error here: you using alpa beta = 1; gamma = 3; de...

2 years ago | 0

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Answered
¿Por qué mi código no corre?
Hola, Creo que tu condicion incial debe ser de solo dos elementos y no de tres. Intenta este programa principal, el cual llamará...

2 years ago | 0

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