How can I choose certain parameters to choose different ways to calculate the determinant?

% A
A = [3 34; 23 1] % Create matrix
det(A) % Calculate determinant

%B
ad = 3*1 % Defining first diagonal AD
cb = 23*34 % Defining second diagonal CB
ad-cb % Calculating the determinant


%C
% Defining variables
a = 5
b = 64
c = 32
d = 43
e = 51
f = 23
g = 70
h = 8
i = 14
% Creating Matrix M from variables
M = [a b c; d e f; g h i]
% Defining the forward diagonals
aei = a*e*i
bfg = b*f*g
cdh = c*d*h
% Defining the backward diagonals
afh = a*f*h
bdi = b*d*i
ceg = c*e*g
% Calculating determinant
detM = aei+bfg+cdh-afh-bdi-ceg

% D
if ndims (A)==2 && (size(A,1)==size(A,2)) % checking if the dimensions are squared
    disp("The matrix is Square") % success message
    det(A)
else disp("The matrix is not square") % error message
end

In exercise D I need to have two input variables. first one the matrix and second one a variable to select the way the determinant is calculated.

I am struggeling with finding a way to input the second variable.

Additionally I first need to check if the array is sqared, and depending if it is square I need to calculate the determinant. (I ve already done this I think haha).

Can some one help me?

Answer 1

[Voss]

Below is a function get_det, made by adapting your code, which takes a matrix as its first input and a character vector specifying a method as its second input.

Here are some lines of code calling the function with different inputs:

M = [1 2; 3 4];

detM = get_det(M)

The matrix is Square

detM = -2

detM = get_det(M,'B')

The matrix is Square

detM = -2

detM = get_det(M,'C')

The matrix is Square
For method C, matrix must be 3-by-3. Using method A instead.

detM = -2

detM = get_det(M,'foo')

The matrix is Square
Unrecognized method: foo

detM = NaN

M = [5 64 32; 43 51 23; 70 8 14];

detM = get_det(M)

The matrix is Square

detM = -36070

detM = get_det(M,'B')

The matrix is Square
For method B, matrix must be 2-by-2. Using method A instead.

detM = -36070

detM = get_det(M,'C')

The matrix is Square

detM = -36070

detM = get_det()

The matrix is Square

detM = -779

detM = get_det([3 34; 23 1])

The matrix is Square

detM = -779

detM = get_det([1 2 3])

Error using solution>get_det
The matrix is not square

The function:

function out = get_det(A,method)

if ~nargin
    A = [3 34; 23 1]; % Create default matrix, if none given
end

if ndims (A)==2 && (size(A,1)==size(A,2)) % checking if the matrix is square
    disp("The matrix is Square") % success message
else
%     disp("The matrix is not square") % error message
    error("The matrix is not square") % error message
end

if nargin < 2
    method = 'A';
end

if strcmp(method,'B') && size(A,1) ~= 2
    disp('For method B, matrix must be 2-by-2. Using method A instead.')
    method = 'A';
elseif strcmp(method,'C') && size(A,1) ~= 3
    disp('For method C, matrix must be 3-by-3. Using method A instead.')
    method = 'A';
end

switch method
    case 'A' %A
        out = det(A); % Calculate determinant
    case 'B' %B
        ad = A(1,1)*A(2,2); % Defining first diagonal AD
        cb = A(1,2)*A(2,1); % Defining second diagonal CB
        out = ad-cb; % Calculating the determinant
    case 'C' %C
        % Defining the forward diagonals
        aei = A(1,1)*A(2,2)*A(3,3);
        bfg = A(1,2)*A(2,3)*A(3,1);
        cdh = A(1,3)*A(2,1)*A(3,2);
        % Defining the backward diagonals
        afh = A(1,1)*A(2,3)*A(3,2);
        bdi = A(1,2)*A(2,1)*A(3,3);
        ceg = A(1,3)*A(2,2)*A(3,1);
        % Calculating determinant
        out = aei+bfg+cdh-afh-bdi-ceg;
    otherwise
        disp(sprintf('Unrecognized method: %s',method));
        out = NaN;
end

end

[Jonas Morgner]

Hey, first of all thank you so much for the code, however I still get an error when entering the code:

Error: Function definition are not supported in this

context. Functions can only be created as local or

nested functions in code files.

How can I fix this?

[Voss]

The function get_det should be in an m-file.

Probably it's best to make a new m-file, copy the definition of the function get_det (i.e., everything in my answer from the line function out = get_det(A,method) until the end), paste that into the m-file, and save the file as get_det.m