uses of 'zeros' and 'ones' function ?

hello all, what are the main uses of functions 'zeros' and 'ones' ? Why we use them ? thank you

Answer 1

[James Tursa]

A couple of examples.

zeros is often used to allocate a variable to a known size, then downstream code will fill in the individual elements. E.g.,

x = zeros(1,5);  % Pre-allocate x to the correct size
for k=1:5
    x(k) = k^2;  % Fill in the individual elements
end

ones could be used to allocate a variable with a constant. E.g.,

x = ones(1,5) * 7;  % Allocate a variable and fill it with 7's

[Stephen23]

Array preallocation is described very well in the documentation:

http://www.mathworks.com/help/matlab/matlab_prog/techniques-for-improving-performance.html

http://blogs.mathworks.com/loren/2012/11/29/understanding-array-preallocation/

Understanding array preallocation is critical for writing efficient loops in MATLAB.

[Marcus Sandquist Lignell]

In addition to this, when using for loops; pre-allocating a matrix in the correct size for the output results will speed up your solve time.

[yogesh jain]

Thank you very much all (Mr. James Tursa ,Stephen Cobeldick and Marcus Sandquist Lignell) . That was pretty useful :)

Answer 2

[Dimithra Anton]

zeros(length(numbers),2)

what about this??? what does (numbers) do and why is the number of columns 6?

[Steven Lord]

numbers is an array that is being passed into the length function (or it is a function that can be called with no input arguments and whose first output is being passed into the length function.)

I would not expect that command to return an array with six columns. Assuming you haven't written or downloaded a zeros.m function that is taking precedence over the built-in function it should return a matrix with two columns.

which -all zeros