MATLAB Central Newsreader - usage of " . " in these two equations !!!

usage of " . " in these two equations !!!

Kuo-Hsien — Wed, 18 Feb 2009 03:02:02 -0500

Dear all,
I got the following error message:

??? Error using ==> mrdivide
Out of memory. Type HELP MEMORY for your options.

Error in ==> weather4Elora at 57
ec_sh_06=0.622*ec_es_06/(ec_p_06-0.378*ec_es_06);

However, I thought I probably the equation need to be modified to the following one.
ec_sh_06=(0.622.*ec_es_06)./(ec_p_06-0.378.*ec_es_06);

What is the difference between these two equations? Why do we need to put a " . " behind numbers? Can you guys help me to under this usage?

Thanks,
Michael

Re: usage of " . " in these two equations !!!

Matt Fig — Wed, 18 Feb 2009 03:43:02 -0500

"Kuo-Hsien" <mchangks@hotmail.com> wrote in message
> What is the difference between these two equations? Why do we need to put a " . " behind numbers? Can you guys help me to under this usage?

The dot is read as 'element-by-element' when used like this. Study an easy example if it is still unclear to you.

A = magic(2)
A^2
A*A
A.^2

Now, which one to use in your application will depend on what you are trying to do.

M`Ekbe[W&MOkkakQ\Q9kkr[rTQ1[`kN`UXyMTMYk\NMZT[[SOUX,[QaMMYZ

Re: usage of " . " in these two equations !!!

Greg — Thu, 19 Feb 2009 14:57:02 -0500

"Matt Fig" <spamanon@yahoo.com> wrote in message <gng046$quc$1@fred.mathworks.com>...
> "Kuo-Hsien" <mchangks@hotmail.com> wrote in message
> > What is the difference between these two equations? Why do we need to put a " . " behind numbers? Can you guys help me to under this usage?
>
>
> The dot is read as 'element-by-element' when used like this. Study an easy example if it is still unclear to you.
>
> A = magic(2)
> A^2
> A*A
> A.^2
>
> Now, which one to use in your application will depend on what you are trying to do.
>
>
>
>
> M`Ekbe[W&MOkkakQ\Q9kkr[rTQ1[`kN`UXyMTMYk\NMZT[[SOUX,[QaMMYZ

For more information regarding MATLAB operators, go to the Section titled "Operators" at the following web address:

http://www.mathworks.com/access/helpdesk/help/techdoc/matlab.html

Re: usage of " . " in these two equations !!!

someone — Thu, 19 Feb 2009 16:22:01 -0500

"Kuo-Hsien" <mchangks@hotmail.com> wrote in message <gnftna$jud$1@fred.mathworks.com>...
> Dear all,
> I got the following error message:
>
> ??? Error using ==> mrdivide
> Out of memory. Type HELP MEMORY for your options.
>
> Error in ==> weather4Elora at 57
> ec_sh_06=0.622*ec_es_06/(ec_p_06-0.378*ec_es_06);
>
>
> However, I thought I probably the equation need to be modified to the following one.
> ec_sh_06=(0.622.*ec_es_06)./(ec_p_06-0.378.*ec_es_06);
>
> What is the difference between these two equations? Why do we need to put a " . " behind numbers? Can you guys help me to under this usage?
>
> Thanks,
> Michael

Besides what others have already replied, you don't "need" the dots behind numbers (scalars). But you do "need" them before the slash (divide) in your case above.

Re: usage of " . " in these two equations !!!

Kuo-Hsien — Thu, 19 Feb 2009 16:51:02 -0500

Here is my test as below. By the way, I deeply thank those who advice me in Matlab.

So, I need to put a "." before any divides, not after scalers.

>> ec_es_06=[1;2;3;4;5]
>> ec_p_06=[4;5;6;7;8]
>> nodot=0.622*ec_es_06/(ec_p_06-0.378*ec_es_06)

nodot =

         0 0 0 0 0.1018
         0 0 0 0 0.2036
         0 0 0 0 0.3054
         0 0 0 0 0.4072
         0 0 0 0 0.5090
>> number_dot=(0.622.*ec_es_06)./(ec_p_06-0.378.*ec_es_06)

number_dot =

    0.1717
    0.2931
    0.3835
    0.4534
    0.5090

>> divide_dot=(0.622.*ec_es_06)./(ec_p_06-0.378*ec_es_06)

divide_dot =

    0.1717
    0.2931
    0.3835
    0.4534
    0.5090