I am pretty beginner in Octave. I try to solve an ODE. The code is below.
I got always the following error message:
error: operator /: nonconformant arguments (op1 is 1x1, op2 is 0x0)
Do You have any idea what should I modify?
Thanks a lot
close all;
clear all;
Ap = 5.66;
mp_gl = 5;
alfa_l = 2.5;
c_gl = 3200;
c_m = 3800;
T_inf = 17;
t_1_SI=3600;
m_must=1070;
T_m_0 = 18;
#
#
t_ODE1=[0, t_1_SI];
# Solve ODE
function dtT_must = ODE1(t,T_must)
global alfa_l;
global T_inf;
global Ap;
global c_gl;
global mp_gl;
global c_m;
global m_must;
dtT_must = (alfa_l*(T_inf-T_must)*Ap-c_gl*mp_gl)/(c_m*m_must);
endfunction
[t,T_must] = ode45 (#ODE1, t_ODE1, T_m_0);
Related
I am trying to implement the secant method using Octave, and in particular I made a function called secant("function","x0","x1","tolerance"). I used the while-loop for calculate the root of a function and I think the problem is in the loop.
But the result that I get, it is not what I expect. The correct answer is x=0,49438.
My code is the following:
tol = 10.^(-5); # tolerance
x0 = 0.4; # initial point
x1 = 0.6; # initial point
syms x;
fun = #(x) exp(sin(x)) - 2/(1+x.^2); # f(x) = exp(sin(x)) - 2/(1+x^2)
fprintf("Function f(x)\n");
fun
fprintf("\n");
fprintf("initial points: %f\n",x0,x1);
function[raiz,errel,niter] = secant(fun,x0,x1,tol)
niter = 0; # steps number
errel = []; # the vector of relative errors
y0 = fun(x0); # f(x0)
y1 = fun(x1); # f(x1)
ra = 0.0; # ra is the variable of the function's root
while abs(ra-x1)>= tol
niter += 1;
ra = x1 - ((x1-x0)./(y1-y0)).*y0; # formula of the secant method
if abs((ra-x1))<tol
raiz = ra;
return;
endif
x0 = x1; y0 = y1; x1 = ra;
y1 = fun(ra);
errel(niter) = abs(ra-x1)/abs(ra); # Calcule of relative error
endwhile
if abs((ra-x1)/ra)<tol
fprintf ('The method is over\n');
fprintf ('\n');
endif
raiz = ra;
endfunction
[r,er,tot] = secant(fun,x0,x1,tol)
I appreciate the help you can give me
It makes little sense to use the secant root in the loop condition. At first it is not defined, and inside the loop it is shifted into the support points for the next secant. Note that at the end ra and x1 contain the same value, making the loop condition trivial, in a wrong way.
Next, the secant has the equation
y(x) = y1 + (y1-y0)/(x1-x0)*(x-x_1)
check that with this formula y(x0)=y0 and y(x1)=y1. Thus the secant root is to be found at
x = x1 - (x1-x0)/(y1-y0)*y1
Finally, at no point are symbolic expressions used, defining x as symbolic variable is superfluous.
The break-out test inside the loop is also redundant and prevents a coherent state after the loop. Just remove it and remember that x1 contains the last approximation.
With all this I get an execution log as follows:
Function f(x)
fun =
#(x) exp (sin (x)) - 2 / (1 + x .^ 2)
initial points: 0.400000
initial points: 0.600000
The method is over
r = 0.494379048216965
er =
2.182723270633349e-01 3.747373180587413e-03 5.220701832080676e-05 1.899377363987941e-08
tot = 4
Code:
function result = assess_polynomial_n(y,n)
[coeff, t, pred_accum] = fit_data(y, n);
[avg, std_dev] = compute_error(coeff,y);
[coeff1, t, pred_accum1] = fit_data(y, n+1);
[avg1, std_dev1] = compute_error(coeff1,y);
if avg1>avg
result = n;
elseif avg<0.1 && std_dev<0.1
result = n;
elseif pred_accum1.*(1)<0.0001
result = n;
else
result = 0;
end
end
***Error***
error: compute_error: operator -: nonconformant arguments (op1 is 1x12, op2 is 1x3)
error: called from
compute_error at line 11 column 17
assess_polynomial_n at line 19 column 18
__tester__.octave at line 38 column 1
Does anyone know why I could be getting this error? We're supposed to be working in MATLAB but pasting our code into Moodle which uses Octave if that clears anything up.
I also will post the functions I'm calling for reference since the error is occurring in Compute_Error. This is a part of an overall project where I was to define the functions I'm calling before creating assess_polynomial_n.
function [coeff, t, pred_accum] = fit_data(y, n)
len = length(y);
t = 10*[0:len-1];
coeff = polyfit(t, y, n);
pred_accum = polyval(coeff, t);
end
function [avg std_dev] = compute_error(x,y)
s=[];
for i=1:length(x)
error=abs(x(i)-y(i));
s=[s,error];
end
avg = mean(s);
std_dev = std(s);
end
The problem lies in this line of code:
[avg1, std_dev1] = compute_error(coeff1,y);
You are trying to compute the error between the original data and the coefficients of the fitted polynomial. It doesn't make sense, right?
Instead, you should compute the error between the original data and the fitted data, which is the polynomial's output at each t value. The correct code would be:
[avg1, std_dev1] = compute_error(pred_accum1,y);
I am trying to solve the following two equations using Octave:
eqn1 = (wp/Cwc)^(2*N) - (1/10^(0.1*Ap))-1 == 0;
eqn2 = (ws/Cwc)^(2*N) - (1/10^(0.1*As))-1 == 0;
I used the following code:
syms Cwc N
eqn1 = (wp/Cwc)^(2*N) - (1/10^(0.1*Ap))-1 == 0;
eqn2 = (ws/Cwc)^(2*N) - (1/10^(0.1*As))-1 == 0;
sol = solve(eqn1 ,eqn2, Cwc, N)
ws,wp,As, and Ap are given as 1.5708, 0.31416, 0.5, 45 respectively.
But I am getting the following error:
error: Python exception: NotImplementedError: could not solve
126491*(pi*(3*10**N*sqrt(314311)*pi**(-N)/1223)**(1/N)/2)**(2*N) - 126495
occurred at line 7 of the Python code block:
d = sp.solve(eqs, *symbols, dict=True)
What should I do to solve this?
Edit:
I modified the equations a little bit.
pkg load symbolic
clear all
syms Cwc N
wp = 0.31416
ws = 1.5708
As = 45
Ap = 0.5
eqn2 = N - log10(((1/(10^(0.05*As)))^2)-1)/2*log10(ws/Cwc) == 0;
eqn1 = N - log10(((1/(10^(0.05*Ap)))^2)-1)/2*log10(wp/Cwc) == 0;
sol = solve(eqn1,eqn2,Cwc,N)
And now I am getting this error:
error: Python exception: AttributeError: MutableDenseMatrix has no attribute is_Relational.
occurred at line 3 of the Python code block:
if arg.is_Relational:
Looking at the equations, with unknowns in the base and exponent of the same term, highly suggests there is no symbolic solution to be found. I gave a simplified system (2/x)^y = 4, (3/x)^y = 5 to a couple of symbolic solvers, neither of which got anything from it. So, the only way to solve this is numerically (which makes sense because the four known parameters you have are some floating point numbers anyway). Octave's numeric solver for this purpose is fsolve. Example of usage:
function y = f(x)
Cwc = x(1);
N = x(2);
ws = 1.5708;
wp = 0.31416;
As = 0.5;
Ap = 45;
y = [(wp/Cwc)^(2*N) - (1/10^(0.1*Ap))-1; (ws/Cwc)^(2*N) - (1/10^(0.1*As))-1];
endfunction
fsolve(#f, [1; 1])
(Here, [1; 1] is an initial guess.) The output is
0.31413
0.19796
I am trying to solve a system of two ODEs using Octave, and in particular the function lsode.
The code is the following:
function xdot = f (x,t)
a1=0.00875;
a2=0.075;
b1=7.5;
b2=2.5;
d1=0.0001;
d2=0.0001;
g=4*10^(-8);
K1=5000;
K2=2500;
n=2;
m=2;
xdot = zeros(2,1);
xdot(1) = a1+b1*x(1)^n/(K1^n+x(1)^n)-g*x(1)*x(2)-d1*x(1);
xdot(2) = a2+b2*x(1)^m/(K2^m+x(1)^m)-d2*x(2);
endfunction
t = linspace(0, 5000, 200)';
x0 = [1000; 1000];
x = lsode ("f", x0, t);
set term dumb;
plot(t,x);
I am getting continuously the same error, that "x" is not defined, and I do not know why. The error is the following:
warning: function name 'f' does not agree with function file name '/home /Simulation 1/sim.m'
error: 'x' undefined near line 17 column 17
error: called from
sim at line 17 column 9
It would we great that any of you could help me with this code.
You have two errors. One, you are not saving your source code with the proper name. Two, variable "x" is a vector, and nothing in your script indicates that. You should add a line "x = zeros(1,2);" right after "xdot = zeros(2,1);".
Try the following code:
function ODEs
t = linspace(0, 5000, 200);
x0 = [1000; 1000];
x = lsode (#f, x0, t);
fprintf('t = %e \t\t x = %e\n',t,x);
endfunction
function xdot = f(x,t)
a1=0.00875;
a2=0.075;
b1=7.5;
b2=2.5;
d1=0.0001;
d2=0.0001;
g=4*10^(-8);
K1=5000;
K2=2500;
n=2;
m=2;
xdot = zeros(2,1);
x = zeros(1,2);
xdot(1) = a1+b1*x(1)^n/(K1^n+x(1)^n)-g*x(1)*x(2)-d1*x(1);
xdot(2) = a2+b2*x(1)^m/(K2^m+x(1)^m)-d2*x(2);
endfunction
Save it as ODEs.m and execute it. It does not plot anything, but gives you an output with the results for the t range you supplied.
I am new to Octave although I can say I am an expert Matlab user. I am running Octave on a Linux server (Red Hat) remotely through PuTTY, from a windows machine.
I am observing a very strange behavior in Octave. I call myfun(a) which performs as expected giving the sought results. Now, if I run, say, myfun(b) with b!=a, I get again myfun(a). Clear -f does not solve the problem. I need to reboot octave to change the parameters.
What am I doing wrong?
Thanks a lot
Francesco
This is the code for the function I mentioned:
function [a, v, obj, infos, iter] = mle_garch( p )
#{
% this function estimates the GARCH(1,1) parameters
% it is assumed we pass the adjusted price level p
#}
global y = (diff(log(p))-mean(diff(log(p))))*100;
global h = zeros(size(y));
a0 = [var(y)*0.9; 0.8; 0.1];
[a, obj, infos, iter] = sqp(a0, #loglike_garch, [], #loglike_con, [], [], 1000);
v = sqrt(h * 260);
endfunction
function g = loglike_garch( a )
global y h
n = length(y);
h(1) = var(y);
for i = 2 : n,
h(i) = a(1) + a(2) * h(i-1) + a(3) * y(i-1)^2;
endfor
g = 0.5 * ( sum(log(h)) + sum(y.^2./h) ) / n;
endfunction
function f = loglike_con( a )
f = [1;0;0;0] + [0 -1 -1;eye(3)] * a;
endfunction
I'm assuming the myfun you mentioned is mle_garch. The problem is the way you're initializing the global h and v variables (do you really need them to be global?). When you have a piece of code like this
global y = (diff(log(p))-mean(diff(log(p))))*100;
global h = zeros(size(y));
the values of y and h are defined the first time only. You can change their values later on, but this specific lines will never be ran again. Since your code only uses the input argument to define these two variables, the value which you use to run the function the first time will be used every single other time. If you really want to keep those variables global, replace it with the following:
global y;
global h;
y = (diff(log(p))-mean(diff(log(p))))*100;
h = zeros(size(y));
But I don't see any reason to keep them global so just don't make them global.
Also, you mentioned this code worked fine in Matlab. I was under the impression that you couldn't initialize global and persistent variables in Matlab which would make your code illegal in Matlab.