I am not very used to MATLAB and I'm trying to solve the following problem using MATLAB ode45, however, it's not working.
I was working on a problem in reaction engineering, using a Semi-Batch Reactor.
The reaction is given by
A + B ---> C + D
A is placed in the reactor and B is being continuously added into the reactor with a flowrate of v0 = 0.05 L/s. Initial volume is V0 = 5 L. The reaction is elementary. The reaction constant is k = 2.2 L/mol.s.
Initial Concentrations: for A: 0.05 M, for B: 0.025 M.
Performing a mole balance of each species in the reactor, I got the following 4 ODEs, and the expression of V (volume of the reactor is constantly increasing)
Solving this system and plotting the solution against time, I should get this
Note that plots of C(C) and C(D) are the same.
And let's set tau = v0/V.
Now for the MATLAB code part.
I have searched extensively online, and from what I've learned, I came up with the following code.
First, I wrote the code for the ODE system
function f = ODEsystem(t, y, tau, ra, y0)
f = zeros(4, 1);
f(1) = ra - tau*y(1);
f(2) = ra + tau*(y0(2) - y(2));
f(3) = -ra - tau*y(3);
f(4) = -ra - tau*y(4);
end
Then, in the command window,
t = [0:0.01:5];
v0 = 0.05;
V0 = 5;
k = 2.2;
V = V0 + v0*t;
tau = v0./V;
syms y(t);
ra = -k*y(1)*y(2);
y0 = [0.05 0.025 0 0];
[t, y] = ode45(#ODEsystem(t, y, tau, ra, y0), t, y0);
plot(t, y);
However, I get this...
Please if anyone could help me fix my code. This is really annoying :)
ra should not be passed as parameter but be computed inside the ODE system. V is likewise not a constant. Symbolic expressions should be used for formula transformations, not for numerical methods. One would also have to explicitly evaluate the symbolic expression at the wanted numerical values.
function f = ODEsystem(t, y, k, v0, V0, cB0)
f = zeros(4, 1);
ra = -k*y(1)*y(2);
tau = v0/(V0+t*v0);
f(1) = ra - tau*y(1);
f(2) = ra + tau*(cB0 - y(2));
f(3) = -ra - tau*y(3);
f(4) = -ra - tau*y(4);
end
Then use the time span of the graphic, start with all concentrations zero except for A, use the concentration B only for the inflow.
t = [0:1:500];
v0 = 0.05;
V0 = 5;
k = 2.2;
cB0 = 0.025;
y0 = [0.05 0 0 0];
[t, y] = ode45(#(t,y) ODEsystem(t, y, k, v0, V0, cB0), t, y0);
plot(t, y);
and get a good reproduction of the reference image
I have always used R, so I am quite new to Matlab and running into some troubleshooting issues. I am running some code for a tensor factorization method (available here: https://github.com/caobokai/tBNE). To start I tried to run the demo code, which generates simulated data to run the method with, which results in the following error(s):
Error using feval
Undefined function or variable 'Sfun'.
Error in OptStiefelGBB (line 199)
[F, G] = feval(fun, X , varargin{:}); out.nfe = 1;
Error in tbne_demo>tBNE_fun (line 124)
S, #Sfun, opts, B, P, X, L, D, W, Y, alpha, beta);
Here is the block of code I am running:
clear
clc
addpath(genpath('./tensor_toolbox'));
addpath(genpath('./FOptM'));
rng(5489, 'twister');
m = 10;
n = 10;
k = 10; % rank for tensor
[X, Z, Y] = tBNE_data(m, n, k); % generate the tensor, guidance and label
[T, W] = tBNE_fun(X, Z, Y, k);
[~, y1] = max(Y, [], 2);
[~, y2] = max(T{3} * W, [], 2);
fprintf('accuracy %3.2e\n', sum(y1 == y2) / n);
function [X, Z, Y] = tBNE_data(m, n, k)
B = randn(m, k);
S = randn(n, k);
A = {B, B, S};
X = ktensor(A);
Z = randn(n, 4);
Y = zeros(n, 2);
l = ceil(n / 2);
Y(1 : l, 1) = 1;
Y(l + 1 : end, 2) = 1;
X = tensor(X);
end
function [T, W] = tBNE_fun(X, Z, Y, k)
% t-BNE computes brain network embedding based on constrained tensor factorization
%
% INPUT
% X: brain networks stacked in a 3-way tensor
% Z: side information
% Y: label information
% k: rank of CP factorization
%
% OUTPUT
% T is the factor tensor containing
% vertex factor matrix B = T{1} and
% subject factor matrix S = T{3}
% W is the weight matrix
%
% Example: see tBNE_demo.m
%
% Reference:
% Bokai Cao, Lifang He, Xiaokai Wei, Mengqi Xing, Philip S. Yu,
% Heide Klumpp and Alex D. Leow. t-BNE: Tensor-based Brain Network Embedding.
% In SDM 2017.
%
% Dependency:
% [1] Matlab tensor toolbox v 2.6
% Brett W. Bader, Tamara G. Kolda and others
% http://www.sandia.gov/~tgkolda/TensorToolbox
% [2] A feasible method for optimization with orthogonality constraints
% Zaiwen Wen and Wotao Yin
% http://www.math.ucla.edu/~wotaoyin/papers/feasible_method_matrix_manifold.html
%% set algorithm parameters
printitn = 10;
maxiter = 200;
fitchangetol = 1e-4;
alpha = 0.1; % weight for guidance
beta = 0.1; % weight for classification loss
gamma = 0.1; % weight for regularization
u = 1e-6;
umax = 1e6;
rho = 1.15;
opts.record = 0;
opts.mxitr = 20;
opts.xtol = 1e-5;
opts.gtol = 1e-5;
opts.ftol = 1e-8;
%% compute statistics
dim = size(X);
normX = norm(X);
numClass = size(Y, 2);
m = dim(1);
n = dim(3);
l = size(Y, 1);
D = [eye(l), zeros(l, n - l)];
L = diag(sum(Z * Z')) - Z * Z';
%% initialization
B = randn(m, k);
P = B;
S = randn(n, k);
S = orth(S);
W = randn(k, numClass);
U = zeros(m, k); % Lagrange multipliers
%% main loop
fit = 0;
for iter = 1 : maxiter
fitold = fit;
% update B
ete = (S' * S) .* (P' * P); % compute E'E
b = 2 * ete + u * eye(k);
c = 2 * mttkrp(X, {B, P, S}, 1) + u * P + U;
B = c / b;
% update P
ftf = (S' * S) .* (B' * B); % compute F'F
b = 2 * ftf + u * eye(k);
c = 2 * mttkrp(X, {B, P, S}, 2) + u * B - U;
P = c / b;
% update U
U = U + u * (P - B);
% update u
u = min(rho * u, umax);
% update S
tic;
[S, out] = OptStiefelGBB(...
S, #Sfun, opts, B, P, X, L, D, W, Y, alpha, beta);
tsolve = toc;
fprintf(...
['[S]: obj val %7.6e, cpu %f, #func eval %d, ', ...
'itr %d, |ST*S-I| %3.2e\n'], ...
out.fval, tsolve, out.nfe, out.itr, norm(S' * S - eye(k), 'fro'));
% update W
H = D * S;
W = (H' * H + gamma * eye(k)) \ H' * Y;
% compute the fit
T = ktensor({B, P, S});
normresidual = sqrt(normX ^ 2 + norm(T) ^ 2 - 2 * innerprod(X, T));
fit = 1 - (normresidual / normX);
fitchange = abs(fitold - fit);
if mod(iter, printitn) == 0
fprintf(' Iter %2d: fitdelta = %7.1e\n', iter, fitchange);
end
% check for convergence
if (iter > 1) && (fitchange < fitchangetol)
break;
end
end
%% clean up final results
T = arrange(T); % columns are normalized
fprintf('factorization error %3.2e\n', fit);
end
I know that there is little context here, but my suspicion is that I need to have Simulink, as Sfun is a Simulink related function(?). The script requires two toolboxes: tensor_toolbox, and FOptM.
Available at:
https://www.sandia.gov/~tgkolda/TensorToolbox/index-2.6.html
https://github.com/andland/FOptM
Thank you so much for your help,
Paul
Although SFun is an often used abbreviation for a Simulink S-Function, in this case the error has nothing to do with Simulink, and the name is a coincidence. (There is no Simulink related function specifically called Sfun, it is just a general term.)
Your error message has #Sfun in it, which is a way in MATLAB of creating a function handle to an (m-code) function called Sfun. I'd summize from the code you've shown that this is a cost function used in the optimization.
If you look at the code that your code is based on (tBNE_fun.m) you'll see that there is a function at the end of the file called Sfun. It is this that you are missing.
I am trying to code a ML algorithm in Matlab. These are my different functions:
sigmoid.m:
function g = sigmoid(z)
g = zeros(size(z));
g = 1 ./ (1+exp(z));
costFunction.m
function [J, grad ] = costFunction(theta, X, y)
m = length(y); % number of training examples
z = -X * theta;
g = sigmoid(z);
J = 1/m * ((-y * log(g)') - ((1 - y) * log(1 - g)'));
grad = zeros(size(theta'));
grad = (1/m) * (X' * (g - y));
ex2.m (This is the main file of my project and I put the relative lines I get this error message)
options = optimset('GradObj', 'on', 'MaxIter', 400);
[theta, cost] = ...
fminunc(#(t)(costFunction(t, X, y)), initial_theta, options);
The error message:
Error using fminunc (line 348) Supplied objective function must return
a scalar value.
Error in ex2 (line 97) fminunc(#(t)(costFunction(t, X, y)),
initial_theta, options);
I don't know is there enough information above or not? If not, let me know to add extra information.
I changed the following line of code:
J = 1/m * ((-y * log(g)') - ((1 - y) * log(1 - g)'));
To the following line of code:
J = 1/m * (((-y)' * log(g)) - ((1 - y)' * log(1 - g)));
And problem solved!
The y and g were 100*1 matrices and with previous code I had J=100*100 matrix, but with new code I have J=1*1 matrix or scalar number and problem solved!
I am taking the course from Andrew Ng on Machine Learning on Coursera. In this assginment, I am working to calculate the cost function using logistic regression in MatLab, but am receiving "Error using sfminbx (line 27)
Objective function is undefined at initial point. fminunc cannot continue.".
I should add that the cost J within the costFunction function below is NaN because the log(sigmoid(X * theta)) is a -Inf vector. I'm sure this is related to the exception. Can you please help?
My cost function looks like the following:
function [J, grad] = costFunction(theta, X, y)
m = length(y); % number of training examples
J = 0;
grad = zeros(size(theta));
h = sigmoid(theta * X);
J = - (1 / m) * ((log(h)' * y) + (log(1 - h)' * (1 - y)));
grad = (1 / m) * X' * (h - y);
end
My code that calls this function looks like the following:
data = load('ex2data1.txt');
X = data(:, [1, 2]); y = data(:, 3);
[m, n] = size(X);
% Add intercept term to x and X_test
X = [ones(m, 1) X];
% Initialize fitting parameters
initial_theta = zeros(n + 1, 1);
% Compute and display initial cost and gradient
[cost, grad] = costFunction(initial_theta, X, y);
fprintf('Cost at initial theta (zeros): %f\n', cost);
fprintf('Expected cost (approx): 0.693\n');
fprintf('Gradient at initial theta (zeros): \n');
fprintf(' %f \n', grad);
fprintf('Expected gradients (approx):\n -0.1000\n -12.0092\n -11.2628\n');
% Compute and display cost and gradient with non-zero theta
test_theta = [-24; 0.2; 0.2];
[cost, grad] = costFunction(test_theta, X, y);
fprintf('\nCost at test theta: %f\n', cost);
fprintf('Expected cost (approx): 0.218\n');
fprintf('Gradient at test theta: \n');
fprintf(' %f \n', grad);
fprintf('Expected gradients (approx):\n 0.043\n 2.566\n 2.647\n');
fprintf('\nProgram paused. Press enter to continue.\n');
pause;
%% ============= Part 3: Optimizing using fminunc =============
% In this exercise, you will use a built-in function (fminunc) to find the
% optimal parameters theta.
% Set options for fminunc
options = optimset('GradObj', 'on', 'MaxIter', 400, 'Algorithm', 'trust-
region');
% Run fminunc to obtain the optimal theta
% This function will return theta and the cost
[theta, cost] = ...
fminunc(#(t)(costFunction(t, X, y)), initial_theta, options);
end
The dataset looks like the following:
34.62365962451697,78.0246928153624,0
30.28671076822607,43.89499752400101,0
35.84740876993872,72.90219802708364,0
60.18259938620976,86.30855209546826,1
79.0327360507101,75.3443764369103,1
45.08327747668339,56.3163717815305,0
61.10666453684766,96.51142588489624,1
75.02474556738889,46.55401354116538,1
76.09878670226257,87.42056971926803,1
84.43281996120035,43.53339331072109,1
95.86155507093572,38.22527805795094,0
75.01365838958247,30.60326323428011,0
82.30705337399482,76.48196330235604,1
69.36458875970939,97.71869196188608,1
39.53833914367223,76.03681085115882,0
53.9710521485623,89.20735013750205,1
69.07014406283025,52.74046973016765,1
67.94685547711617,46.67857410673128,0
70.66150955499435,92.92713789364831,1
76.97878372747498,47.57596364975532,1
67.37202754570876,42.83843832029179,0
89.67677575072079,65.79936592745237,1
50.534788289883,48.85581152764205,0
34.21206097786789,44.20952859866288,0
77.9240914545704,68.9723599933059,1
62.27101367004632,69.95445795447587,1
80.1901807509566,44.82162893218353,1
93.114388797442,38.80067033713209,0
61.83020602312595,50.25610789244621,0
38.78580379679423,64.99568095539578,0
61.379289447425,72.80788731317097,1
85.40451939411645,57.05198397627122,1
52.10797973193984,63.12762376881715,0
52.04540476831827,69.43286012045222,1
40.23689373545111,71.16774802184875,0
54.63510555424817,52.21388588061123,0
33.91550010906887,98.86943574220611,0
64.17698887494485,80.90806058670817,1
74.78925295941542,41.57341522824434,0
34.1836400264419,75.2377203360134,0
83.90239366249155,56.30804621605327,1
51.54772026906181,46.85629026349976,0
94.44336776917852,65.56892160559052,1
82.36875375713919,40.61825515970618,0
51.04775177128865,45.82270145776001,0
62.22267576120188,52.06099194836679,0
77.19303492601364,70.45820000180959,1
97.77159928000232,86.7278223300282,1
62.07306379667647,96.76882412413983,1
91.56497449807442,88.69629254546599,1
79.94481794066932,74.16311935043758,1
99.2725269292572,60.99903099844988,1
90.54671411399852,43.39060180650027,1
34.52451385320009,60.39634245837173,0
50.2864961189907,49.80453881323059,0
49.58667721632031,59.80895099453265,0
97.64563396007767,68.86157272420604,1
32.57720016809309,95.59854761387875,0
74.24869136721598,69.82457122657193,1
71.79646205863379,78.45356224515052,1
75.3956114656803,85.75993667331619,1
35.28611281526193,47.02051394723416,0
56.25381749711624,39.26147251058019,0
30.05882244669796,49.59297386723685,0
44.66826172480893,66.45008614558913,0
66.56089447242954,41.09209807936973,0
40.45755098375164,97.53518548909936,1
49.07256321908844,51.88321182073966,0
80.27957401466998,92.11606081344084,1
66.74671856944039,60.99139402740988,1
32.72283304060323,43.30717306430063,0
64.0393204150601,78.03168802018232,1
72.34649422579923,96.22759296761404,1
60.45788573918959,73.09499809758037,1
58.84095621726802,75.85844831279042,1
99.82785779692128,72.36925193383885,1
47.26426910848174,88.47586499559782,1
50.45815980285988,75.80985952982456,1
60.45555629271532,42.50840943572217,0
82.22666157785568,42.71987853716458,0
88.9138964166533,69.80378889835472,1
94.83450672430196,45.69430680250754,1
67.31925746917527,66.58935317747915,1
57.23870631569862,59.51428198012956,1
80.36675600171273,90.96014789746954,1
68.46852178591112,85.59430710452014,1
42.0754545384731,78.84478600148043,0
75.47770200533905,90.42453899753964,1
78.63542434898018,96.64742716885644,1
52.34800398794107,60.76950525602592,0
94.09433112516793,77.15910509073893,1
90.44855097096364,87.50879176484702,1
55.48216114069585,35.57070347228866,0
74.49269241843041,84.84513684930135,1
89.84580670720979,45.35828361091658,1
83.48916274498238,48.38028579728175,1
42.2617008099817,87.10385094025457,1
99.31500880510394,68.77540947206617,1
55.34001756003703,64.9319380069486,1
74.77589300092767,89.52981289513276,1
The only problem I see is that you should have written h = sigmoid(X * theta) instead of h = sigmoid(theta * X). I am getting the same answer from your code after changing this as I was getting from my code for the same assignment.