# Matlab Misunderstanding

1. Aug 26, 2013

### steve2510

I'm current learning MatLab before i start my second year of engineering and i don't really understand a fundamental aspect of it. My problem is the use of the period "." and when it is deemed to be necessary.

I've looked up what this operator does and found definitions such as Element by element, Point-wise, ect. My problem is these don't mean much to me, I've done work on vectors and matrices, however matrices work consisted of mostly doing practice problems so maybe i don't full understand the fundamentals of matrices. Is there anyway somebody could explain to me what the period operator actually does.

For example why are these two different
y = sqrt(t).*sin(2t);
y = sqrt(t)*sin(2t);

And
y=(3.^x)./(1+3.^x)
y=(3^x )/ (1+3^x)

Any clarification would be much appreciated, thank you.

P.S I hope this is in the right board

2. Aug 26, 2013

### sanka

Dot multiplication .* is used to perform element-by-element array multiplication. An array is either a single row (row vector) or single column (column vector) of some values. For array-array multiplication to work, the arrays must be the same length.

Suppose, you have an array A=[3; 2; 5] which is a 3x1 array and want to multiply it by B=[6; 9; 2] which is another 3x1 array (same lengths), you tell MATLAB to do the following;
Ans=A.*B which multiplies the 2 arrays on an element-by-element basis. This means it multiplies 3x6, 2x9 and 5x2 giving a resultant arry of [18; 18; 10]

Leaving out the dot operator is for matrix multiplication which is differenet.
The 2 examples you provided dont really help to explain the purpose of the dot operator as they are just scalar x scalar examples.
{"found_math": false, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0}