## [Tweets]

**20/02/2019 2:02pm**

RT @leecronin: This is how easy it is to build a modular chemputer that can be programmed to do organic synthesis as described here: https:…

RT @leecronin: This is how easy it is to build a modular chemputer that can be programmed to do organic synthesis as described here: https:…

Here I provide a quick look up of commonly used matrix functions in MATLAB. All of these are compatible with Octave as well.

```
% Produce 2x3 matrix of ones
```

A = ones(2,3)

% Produce 2x3 matrix of twos

A = 2*ones(2,3)

% Produce 2x3 matrix of 0s

A = zeros(2,3)

% Produce 2x3 matrix of random numbers

A = rand(2,3)

% Produce 2x3 matrix of gaussian numbers with mean 0 and variation 1

A = randn(2,3)

% Produce large vector of gaussian numbers

A = -6 + sqrt(10)*(randn(1,10000));

% Print histogram

hist(A)

% Produce 3x3 matrix of random numbers from <-1;1>

A = rand(3,4);

% 5x5 identity matrix

I = eye(5)

% Magic square (all columns, rows, diagonals sum up to same number)

MAGIC = magic(3)

```
% Everything in 2nd column
```

A (:,2)

% Everyting from 1st and 3rd row, all columns

A([1 3],:)

% Append another column vector

A = [A, [100; 101; 102; 103]]

% All elements of A into single column vector

B = A(:)

% Invert matrix

C = pinv(A)

% Transpose matrix

D = C'

% Element-wise multiplication (works with other signs too):

E = rand(2,3)

F = 2*ones(2,3)

G = E .* F

% ElementwiseLogarithm of matrix

log(E)

% Elementwise Exponentiaion

exp(E)

% Element wise minus
E = -E

% Elementwise Absolute values

abs(E)

% Elementwise adding

e = [2;4;5;7]

H = e + ones(length(e),1)

I = E + 1

% Max value of vector

a = [1 34 6 2]

val = max(a)

[val, index] = max(a)

% Element-wise comparison (returns true/false)

a < 3

% Element-wise comparison (returnse elements)

find(a < 3)

% Add up elements

summation = sum(a)

% Mulitply elements

product = prod(a)

% Floor elements

FLOORING = floor(a)

% Ceil elements

CEILING = ceil(a)

% Column- and row- wise maximums where last argument is dimension

columnWiseMaximums = max(A,[],1)

rowWiseMaximums = max(A,[],2)

maximumElement = max(A(:))

% SumUp elements to create vector

sumOfColumns = sum(MAGIC,1)

sumOfRows = sum(MAGIC,2)

% Diagonal sum, first multiply by identity matrix to make all

% elements expect of diagonal 0

MAGIC .* eye(3)

sumOfDiagonal = sum(sum(MAGIC.*eye(3)))

```
% Size of matrix
```

S = size(A)

% Size of rows

S = size(A,1)

% Size of columns

S = size(A,2)

% Size of longer dimension

S = length(A)

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