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

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```//---Inside mexFunction--- //DeclarationsmxArray *zData; int Num;//Copy input pointer z zData = prhs; //Get the IntegerNum = (int)(mxGetScalar(zData)); //print it out on the screenprintf("Your favorite integer is: %d",Num);```

Three data types have been shown here. There are several others and the MATLAB help as well as the MATLAB example code shows how to use them. Now to export the data....

## Returning data to matlab

Assigning return values and data to the left hand side parameters is very similar to getting the data from the last section. The difference here is that memory must be allocated for thedata strucure being used on the output. Here is an example of how to return a 2-D matrix. This code will take the input x and return a copy of the matrix to z0 with every point in x multiplied by 2.Note that I am not copying the name of the output mxArray pointer into another variable.

```//---Inside mexFunction--- //DeclarationsmxArray *xData; double *xValues, *outArray;int i,j; int rowLen, colLen;//Copy input pointer x xData = prhs; //Get matrix xxValues = mxGetPr(xData); rowLen = mxGetN(xData);colLen = mxGetM(xData); //Allocate memory and assign output pointerplhs = mxCreateDoubleMatrix(colLen, rowLen, mxREAL); //mxReal is our data-type//Get a pointer to the data space in our newly allocated memory outArray = mxGetPr(plhs); //Copy matrix while multiplying each point by 2for(i=0;i<rowLen;i++) {for(j=0;j<colLen;j++) {outArray[(i*colLen)+j] = 2*xValues[(i*colLen)+j]; }}```

## Calling built-in functions from a mex-file

While it may be nice to write functions in C, there are so many useful and fast pre-written functions in MATLAB that it would be a crime if we could not use them. Luckily,The Mathworks (creators of MATLAB) has provided this capability. Built-In functions have a parameter list similar to the mexFunction itself. This example uses the built-in function z = conv(x,y);

```//---Inside mexFunction--- //DeclarationsmxArray *result; mxArray *arguments; //Fill in the input parameters with some trasharguments = mxCreateDoubleMatrix(1, 20, mxREAL);arguments = mxCreateDoubleMatrix(1, 10, mxREAL);//In the real world I imagine you would want to actually put //some useful data into the arrays above, but for this example//it doesnt seem neccesary. //Call the FunctionmexCallMATLAB(1,&result,2,arguments,"conv"); //Now result points to an mxArray and you can extract the data as you please!```

## Compiling

Compiling the MEX-Files is similar to compiling with gcc or any other command line compiler. In the MATLAB command prompt, change your current directory to thelocation of the MEX source file. Type: `mex filename.c` into the MATLAB command window. MATLAB may ask you to choose a compiler. Choose the compiler with MATLAB in its directory path.Your function will be called with the same name as your file. (ex: `mex jasonsFunction.c` produces a function that can be called from MATLAB as `[z0,z1] = jasonsFunction(x,y,z);` )

After compiling MATLAB produces the actual MEX binary that can be called as a normal MATLAB function. To call this function, you must be in the same directory with the binary. The binary goes by different namesdepending what system you compiled the source on (ex: Windows=.dll MacOSX=.mexmac Solaris=.mexsol Linux=.mexlx). Your MEX-function will have to be compiled on each type of system that you want to run it on because thebinaries are operating system specific.

## Other useful functions

Here is a nice list of useful functions in the mex library that make life a lot easier. Most of these work in similar fashion to those functions described above. The full list can be found inthe MATLAB help documentation with many examples. There are also some example files in the MATLAB extern directory (MATLAB/extern/examples/mx or mex).

• mxDuplicateArray
• mexErrMsgTxt
• mxMalloc
• mxRealloc
• mxCreateString
• mxDestroyArray
• mxFree
• mxGetCell
• mxGetData
• and many more...

what is math number
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Need help solving this problem (2/7)^-2
x+2y-z=7
Sidiki
what is the coefficient of -4×
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
An investment account was opened with an initial deposit of \$9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
12, 17, 22.... 25th term
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
I'm 13 and I understand it great
AJ
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Atone
hi
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
Vedant
hi vedant can u help me with some assignments
Solomon
find the 15th term of the geometric sequince whose first is 18 and last term of 387
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
hmm well what is the answer
Abhi
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
Augustine
how do they get the third part x = (32)5/4
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
AJ
how
Sheref
can someone help me with some logarithmic and exponential equations.
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
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salma
Commplementary angles
hello
Sherica
im all ears I need to learn
Sherica
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Tamia
hii
Uday
hi
salma
hi
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opoku
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Ali
greetings from Iran
Ali
salut. from Algeria
Bach
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Nharnhar
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Jeannette has \$5 and \$10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
What is the expressiin for seven less than four times the number of nickels
How do i figure this problem out.
how do you translate this in Algebraic Expressions
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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