matlab invalid expression error
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Hi,
I am getting a lot of errors in my code, starting with line 24. Can someone please help me? Thanks!
clear, clc, close all
%%
set(0,'DefaultAxesLineWidth',2,'DefaultLineLineWidth',3)
set(0,'DefaultAxesFontSize',12,'DefaultAxesFontWeight','bold')
%% Generate the data set
% Time values (in seconds)
t = [1 10 10];
% Observed data (in meters)
y = m_true(1) + m_true(2)*t - m_true(3)*t.^2/2 + sigma*randn(10, 1);
% Standard deviation of the errors
sigma = 8 * ones(size(t));
% True model parameters
m_true = [10 100 9.8]; % [m1; m2; m3]
G = [ones(size(t)); t; -0.5 * t.^2];
W = diag(1./(sigma.^2));
m_ls = [G W G'] \ [G W y'];
Cov_m_ls = inv (G W G');
% Degrees of freedom
v = length(t) - length(m_ls);
% Chi-square statistic
chi_square = sum(((y - G' * m_ls) ./ sigma).^2);
p_value = 1 - chi2cdf(chi_square, v); % p-value
% Significance level
% (95% confidence interval)
alpha = 0.05;
% Z-score for alpha
z_alpha = norminv(1 - alpha/2);
confidence_intervals =
[m_ls - z_alpha sqrt(diag(Cov_m_ls)),
m_ls + z_alpha sqrt(diag(Cov_m_ls))];
fprintf('Parameter Estimates (m_ls):\n');
disp(m_ls);\
fprintf('Confidence Intervals (95%%):\n');
disp(confidence_intervals);
fprintf('Chi-Square: %.2f\n', chi_square);
fprintf('Degrees of Freedom: %d\n', v);
fprintf('p-value: %.4f\n', p_value);
t_fit = linspace(min(t), max(t), 100);
% Generate points for the fitted curve
y_fit = m_ls(1) + m_ls(2) t_fit
- (1/2) m_ls(3) * t_fit.^2;
% Fitted model
figure;
plot(t, y, 'o', 'DisplayName', 'Observed Data');
hold on;
plot(t_fit, y_fit, 'r-',
'DisplayName', 'Fitted Model');
xlabel('Time (s)');
ylabel('Distance (m)');
legend('Location', 'Best');
title('Ballistics Regression');
grid on;
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Accepted Answer
Image Analyst
on 1 Oct 2023
Tons of errors. I got tired of fixing them all, but I got this far in your script. You can continue to fix them one at a time as you go down the script:
%%
set(0,'DefaultAxesLineWidth',2,'DefaultLineLineWidth',3)
set(0,'DefaultAxesFontSize',12,'DefaultAxesFontWeight','bold')
%% Generate the data set
% Time values (in seconds)
t = [1 10 10];
numPoints = numel(t);
% True model parameters
m_true = [10 100 9.8]; % [m1; m2; m3]
% Standard deviation of the errors
sigma = 8 * ones(numPoints);
% Observed data (in meters)
y = m_true(1) + m_true(2)*t - m_true(3)*t.^2/2 + sigma .* randn(1, numPoints);
G = [ones(1, numPoints); t; -0.5 * t.^2]
W = diag(1./(sigma.^2))
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More Answers (1)
Sam Chak
on 1 Oct 2023
Hi @Kathleen
Fixed "invalid expression errors" are marked by these arrows ''<--". However, the variable m_true is not provided in the code.
clear, clc, close all
%%
set(0,'DefaultAxesLineWidth',2,'DefaultLineLineWidth',3)
set(0,'DefaultAxesFontSize',12,'DefaultAxesFontWeight','bold')
%% Generate the data set
% Time values (in seconds)
t = [1 10 10];
% Observed data (in meters)
y = m_true(1) + m_true(2)*t - m_true(3)*t.^2/2 + sigma*randn(10, 1);
% Standard deviation of the errors
sigma = 8 * ones(size(t));
% True model parameters
m_true = [10 100 9.8]; % [m1; m2; m3]
G = [ones(size(t)); t; -0.5 * t.^2];
W = diag(1./(sigma.^2));
m_ls = [G W G'] \ [G W y'];
Cov_m_ls = inv([G W G']); % <--
% Degrees of freedom
v = length(t) - length(m_ls);
% Chi-square statistic
chi_square = sum(((y - G' * m_ls) ./ sigma).^2);
p_value = 1 - chi2cdf(chi_square, v); % p-value
% Significance level
% (95% confidence interval)
alpha = 0.05;
% Z-score for alpha
z_alpha = norminv(1 - alpha/2);
confidence_intervals = [m_ls - z_alpha sqrt(diag(Cov_m_ls)), m_ls + z_alpha sqrt(diag(Cov_m_ls))]; % <--
fprintf('Parameter Estimates (m_ls):\n');
disp(m_ls); % <--
fprintf('Confidence Intervals (95%%):\n');
disp(confidence_intervals);
fprintf('Chi-Square: %.2f\n', chi_square);
fprintf('Degrees of Freedom: %d\n', v);
fprintf('p-value: %.4f\n', p_value);
t_fit = linspace(min(t), max(t), 100);
% Generate points for the fitted curve
y_fit = m_ls(1) + m_ls(2)*t_fit - (1/2)*m_ls(3)*t_fit.^2; % <--
% Fitted model
figure;
plot(t, y, 'o', 'DisplayName', 'Observed Data');
hold on;
plot(t_fit, y_fit, 'r-', 'DisplayName', 'Fitted Model'); % <--
xlabel('Time (s)');
ylabel('Distance (m)');
legend('Location', 'Best');
title('Ballistics Regression');
grid on;
1 Comment
Image Analyst
on 1 Oct 2023
It's also weird that the second and third time value are the very same time of 10.
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