# 18.1 Writing c functions in matlab (mex-files)  (Page 2/3)

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## Getting and creating data

The main MATLAB structure used for holding data in MEX-Files is the mxArray. This structure can hold real data, complex data, arrays, matrices, sparse-arrays, strings, and a whole host of other MATLAB data-structures.Using data from some of the basic structures is shown here, but refer to the MATLAB help for using other data structures.

## Get that data

Lets use my example from above (if you forgot: `[z0,z1] = jasonsFunction(x,y,z);` ). Assume that x is a 2-D matrix, y is a string, and z is an integer. Here we wills ee how to extractand use these different types of data.

We have access to the input paramter x by a pointer held in the array prhs. In C, when referencing an array by index, the variable is automatically dereferenced (ie: you dont need to use a star).For clarity, I will copy the variable x over to an mxArray pointer named xData (This does not need to be done for the code to work).

```//---Inside mexFunction--- //DeclarationsmxArray *xData; double *xValues;int i,j; int rowLen, colLen;double avg; //Copy input pointer xxData = prhs[0];//Get matrix x xValues = mxGetPr(xData);rowLen = mxGetN(xData); colLen = mxGetM(xData);//Print the integer avg of each col to matlab console for(i=0;i<rowLen;i++) {avg=0; for(j=0;j<colLen;j++) {avg += xValues[(i*colLen)+j]; //Another Method:// //avg += *xValues++;} avg = avg/colLen;printf("The average of row %d, is %d",i,(int)avg); }```

The function `mxGetPr` is used to get a pointer to the real data xData. This function takes a pointer to an mxArray as the intput paramter, and returns a pointer array of doubles. A similar function `mxGetPi` can be used for complex data. `mxGetN` and `mxGetM` return integers of the lengths of the row and column in the matrix. If this were an array of data, one of thesereturn values would be zero. MATLAB gives the matrix as rows first, then columns (if you were to traverse the matrix linearly) so to jump by position, (x,y) maps to x*colLen+y. MATLAB organizesits arrays this way to reduce cache misses when the row traversal is on the outside loop. It is good to code it this way if you are working for efficiency. `printf()` will print out to the MATLAB command prompt.

Getting a string is very similar, but has its own method. The example below shows the procedure for getting a string. Again, I will copy the input to a pointer called yData.

```//---Inside mexFunction--- //DeclarationsmxArray *yData; int yLength;char *TheString; //Copy input pointer yyData = prhs[1];//Make "TheString" point to the string yLength = mxGetN(yData)+1;TheString = mxCalloc(yLength, sizeof(char)); //mxCalloc is similar to malloc in C mxGetString(yData,TheString,yLength);```

This last example shows how to get a simple integer. This is the method that has always worked for me, but it seems kind of strange so I imagine there is another way to do this.

are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
how did you get the value of 2000N.What calculations are needed to arrive at it
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