I am trying to convert this for loop from matlab to C. Could someone please help

% variables

Fs = 2000;            % Sampling frequency                    
T = 1/Fs;             % Sampling period       
L = 4000;             % Length of signal
t = (0:L-1)*T;          %time samples
A=[16 18 28 33 38 41 59 43 40 58];% Amplitude of noise in dBA (refer to the measurements from consultant)
forigin=[25 31.5 40 50 63 80 100 125 160 200];% Frequency of the noise components (refer to the measurements from consultant)

S=zeros(1,length(t));% This will be the signal representing transformer noise, in your case, it will be the sound created from exciter 

for k=1:length(A)
S = S+10^(A(k)/20)*sin(2*pi*forigin(k)*t);%Creating the transformer noise from the amplitude and frequency components, in your case, it will be the sound created from exciter

end

It is implementing the for loop to C.

I have implemented the variables and the "t" values so far.

Thanks any one who can help

Kay

[Guillaume]

I have implemented the variables and the "t" values so far.

Then show us that bit, as the loop will depends on how they are declared.

[Kay Wonderley]

Hi Guillaume, I am doing this on arduino mega and have been printing out the values of "t". So far I am checking the from the start if i am getting the correct values

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

int L = 4000;
//double t [4000];
//int A [10] = {16 18 28 33 38 41 59 43 40 58};             // an integer array of 10 elements intitialised with values
//double forigin [10] = {25.0 31.5 40.0 50.0 63.0 80.0 100.0 125.0 160.0 200.0};  // a double array of 10 elements intitialised with values

}
void loop()
{
  // put your main code here, to run repeatedly:
int Fs = 2000;
double T = 1/(double)Fs;
 double t[40]; /* t is an array of 4000 integers */
   int i;
   int j;          
   for ( i = 0; i < 40; i++ )/* initialize elements of array t to 0 */  
   {
      t[i] = +(double) i*T; /* set element at location i to i*T */
   }   

     for (j = 0; j < 40; j++ ) /* output each array element's value */
     {
        //Serial.println("Element[%f] = %f\n", j,(float) t[j] );
        //printf( " %f\n", t[j] );

       Serial.print(t[j],15);
       Serial.println("");
         delay(500);
     }

}

Answer 1

[Guillaume]

Note: It's been ages since I've written any C code, and even then it was mostly C++ not C. Expect some bugs.

First you'll have to include the math library whatever that is on Arduino. Usually, it's math.h, so:

#define _USE_MATH_DEFINES  // to force M_PI to exist
#include <math.h>          //for pow, sin and M_PI

The main difficulty with the matlab code is that the operation on S is vectorised which is not an option in C, you have to convert that into a loop, hence you'll have a double for loop.

I would recommend that you name the size of the arrays either using a #define or a variable:

#define TSIZE 40   //or 4000
#define ASIZE 10   //for A and forigin

or

int TSIZE = 40;
int ASIZE = 10;

and use that for all your array declaration

double t[TSIZE];
double A[ASIZE] = {16 18 28 33 38 41 59 43 40 58};  //makes life easier if it's declared as double
double forigin[ASIZE] = {25.0 31.5 40.0 50.0 63.0 80.0 100.0 125.0 160.0 200.0};
//... code to fill t

On to the S calculation:

double S[TSIZE];
int i, k;
//initialise S to 0
for (i = 0; i < TSIZE; ++i) S[i] = 0;
//implement the for k=1:length(A)
for (k = 0; i < 10; ++i){
   //devectorise the S calculation
   for (i = 0; i < TSIZE; ++i){
       S[i] = S[i] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
   }
}

edit: You could move the calculation of pow(10, A[k]/20) out of the i loop since it only depends on k.

[Kay Wonderley]

Thanks This is what I have so far. It is saying that there is a fault expected'}' before numeric constant

#define _USE_MATH_DEFINES  // to force M_PI to exist
#include <math.h>          //for pow, sin and M_PI
#define TSIZE 40   //or 4000

#define ASIZE 10   //for A 
#define FORIGINSIZE 10// SIZE OF forigin
void setup()
{
  // put your setup code here, to run once:
Serial.begin(9600);

int L = 40;
//double t [4000];
//int A [10] = {16 18 28 33 38 41 59 43 40 58};             // an integer array of 10 elements intitialised with values
//double forigin [10] = {25.0 31.5 40.0 50.0 63.0 80.0 100.0 125.0 160.0 200.0};  // a double array of 10 elements intitialised with values

}

void loop() 
{
  double t[TSIZE];
  double A[ASIZE] = {16 18 28 33 38 41 59 43 40 58};  //makes life easier if it's declared as double
  double forigin[ASIZE] = {25.0 31.5 40.0 50.0 63.0 80.0 100.0 125.0 160.0 200.0};

the rest
I would have to change i and k in the other for loops say to m,n ? so it won't get confused?
//... code to fill t  
  int Fs = 2000;
  double T = 1/(double)Fs;
 //double t[40]; /* t is an array of 40 integers */
   int i;
   int j;          
   for ( i = 0; i < 40; i++ )/* initialize elements of array t to 0 */  
   {
      t[i] = +(double) i*T; /* set element at location i to i*T */
   }   

     for (j = 0; j < 40; j++ ) /* output each array element's value */
     {
        //Serial.println("Element[%f] = %f\n", j,(float) t[j] );
        //printf( " %f\n", t[j] );

       Serial.print(t[j],15);
       Serial.println("");
         delay(500);
     }
  double S[TSIZE];
  int i, k;
  //initialise S to 0
  for (i = 0; i < ARRAYSIZE; ++i) 
  {
    S[i] = 0;
  }
  //implement the for k=1:length(A)
  for (k = 0; i <ARRAYSIZE ; ++i)
     {
      A[k] = 0;
     }
     //devectorise the S calculation
     for (i = 0; i < ARRAYSIZE; ++i)
     {
         S[i] = S[i] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
     }

}

[Kay Wonderley]

But thanks you soooo much! this is a big leap forward!!

[Kay Wonderley]

Hi I have the compiling. Commas are needed between array values, I needed to put all variables where the #define was. That way they are all global, abd here is the code Next job is to output the sound w out of the arduino. Thanks so much again.

#define _USE_MATH_DEFINES // to force M_PI to exist #include math.h //for pow, sin and M_PI #define TSIZE 40 //or 4000 #define ASIZE 10 //for A #define FORIGINSIZE 10 // SIZE OF forigin #define ARRAYSIZE 10 // size of S array

int L = 40; double t [40]; double A [10] = {16, 18, 28, 33, 38, 41, 59, 43, 40, 58}; // an integer array of 10 elements intitialised with values double forigin [10] = {25.0, 31.5, 40.0, 50.0, 63.0, 80.0, 100.0, 125.0, 160.0, 200.0}; // a double array of 10 elements intitialised with values int Fs = 2000; int i,j,z,k,v; double T = 1/(double)Fs; double S[TSIZE];

void setup() { // put your setup code here, to run once: Serial.begin(9600); }

void loop() {

   for ( i = 0; i < 40; i++ )/* initialize elements of array t to 0 */  
   {
      t[i] = +(double) i*T; /* set element at location i to i*T */
   }  

   for (j = 0; j < 40; j++ ) /* output each array element's value */
   {

     Serial.print(t[j],15);
     Serial.println("");
     delay(500);
   }
      double S[TSIZE];
      double T = 1/(double)Fs; 
      int z, k,v;
      //initialise S to 0
      for (z = 0; z < ARRAYSIZE; ++z) // I  made int z for zero
      {
        S[z] = 0;
      }
      //implement the for k=1:length(A) k is in the original equation
      for (k = 0; k <ARRAYSIZE ; ++k)
         {
          A[k] = 0;
         }
         //devectorise the S calculation
         for (v = 0; v < ARRAYSIZE; ++v)  // v for vector
         {
          S[v] = S[v] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
         }
  }

[Guillaume]

expected'}' before numeric constant

Sounds like you're missing a closing bracket somewhere. Or some declaration is misplaced. If I remember correctly, in some versions of C (but not C++) variable declarations must all be done at the start of a function.

As I said, expect some bugs. It's been too long since I wrote any C++. In particular there is a bug (which is not the cause of the current error) in that I renamed ARRAYSIZE to TSIZE in some parts but not others. Replace all instances of ARRAYSIZE by TSIZE.

My original loop code should be correct. Your rewritten code does not make much sense, in particular you've taken the second i loop out of the k loop which is completely wrong. As per my original answer it should be

for (k = 0; i < 10; ++i){
   //devectorise the S calculation
   for (i = 0; i < TSIZE; ++i){
       S[i] = S[i] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
   }
}

or if you take out the pow calculation out of the s loop

double apow;  //declaration may need to be at the beggining of the function
for (k = 0; i < 10; ++i){
   apow = pow(10, A[k]/20);
   for (i = 0; i < TSIZE; ++i){
       S[i] = S[i] + apow * sin(2*M_PI*forigin[k]*t[i]);
   }
}

but the i loop should be inside the k loop.

[Kay Wonderley]

Hi I think this is what you mean. However, in Matlab the first values for S are:

0  899.475071494380  1570.91017541897  1861.36356724185  1740.88440906200  1306.16803613629  739.441548916790  238.639601470524  -54.6370978848435

The values for S[i] I get is:

0.00
0.50
0.99
1.47
1.95
2.41
2.86
3.30
3.71
4.10
4.46
4.80
5.10
5.38
5.62
define _USE_MATH_DEFINES  // to force M_PI to exist
#include <math.h>          //for pow, sin and M_PI
#define ASIZE 10   //for A 
#define TSIZE 400   //or 4000
int Fs = 2000;
int L = 40;
double A[ASIZE] = {16, 18, 28, 33, 38, 41, 59, 43, 40, 58};
double forigin[ASIZE] = {25.0, 31.5, 40.0, 50.0, 63.0, 80.0, 100.0, 125.0, 160.0, 200.0};
double S[TSIZE];
double t[TSIZE];
double T = 1/(double)Fs;
int i,k,  j;
//int k = 10;
 double  apow = pow(10, A[k]/20);
void setup() {

    Serial.begin(9600);
  }

void loop()
{
   for ( i = 0; i < TSIZE ; i++ )  /* initialize elements of array t to 0 */  
       {
      t[i] = (double) i*T; /* set element at location i to i*T */
       }
      for (j = 0; j < TSIZE; j++ ) /* output each array element's value */
       {

//      Serial.print(t[j],15);
//     Serial.println("");
//     delay(500);
       } 

//initialise S to 0
for (i = 0; i < TSIZE; ++i) //S[i] = 0;

//implement the for k=1:length(A)

    for (k = 0; i < 10; ++i){
     //devectorise the S calculation
     for (i = 0; i < TSIZE; ++i){
         S[i] = S[i] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
         Serial.print(S[i]);
       Serial.println("");
       delay(500);
     //}
   //}
       //apow;  //declaration may need to be at the beggining of the function
  //for (k = 0; i < 10; ++i){
  //
  //   for (i = 0; i < TSIZE; ++i){
  //       S[i] = S[i] + apow * sin(2*M_PI*forigin[k]*t[i]);
  //        Serial.print(S[i],4);
  //     Serial.println("");
  //     delay(500);
     }
  }
  }

The k value is not incrementing from whaI can see.

Where to from here, any help is appreciated Kind Regards Kay

[Guillaume]

"The k value is not incrementing from whaI can see".

Indeed, because there is a bug in the loop implementation. It should have been

for (k = 0; k < 10; ++k){

or even better

for (k = 0; k < ASIZE; ++k){

instead of

for (k = 0; i < 10; ++i){

As said, expect bugs! I don't have a compiler to test the code.

[Kay Wonderley]

Hi thanks again. I have made the changes but k is not incrementing. K does not seem to be able to see the forigin loop and I don't quite know how.I would appreciate any iseas, or point me to the right place. Kind regards Kay

#define _USE_MATH_DEFINES  // to force M_PI to exist
#include <math.h>          //for pow, sin and M_PI
#define ASIZE 10   //for A 
#define TSIZE 40   //or 4000
int Fs = 2000;
int L = 40;
double A[ASIZE] = {16, 18, 28, 33, 38, 41, 59, 43, 40, 58};
double forigin[ASIZE] = {25.0, 31.5, 40.0, 50.0, 63.0, 80.0, 100.0, 125.0, 160.0, 200.0};
double S[TSIZE];
double t[TSIZE];
double T = 1/(double)Fs;
int i,k,  j;
//int k = 10;
 double  apow = pow(10, A[k]/20);
void setup() {

    Serial.begin(9600);
  }

void loop()
{
   for ( i = 0; i < TSIZE ; i++ )  /* initialize elements of array t to 0 */  
       {
      t[i] = (double) i*T; /* set element at location i to i*T */
       }
      for (j = 0; j < TSIZE; j++ ) /* output each array element's value */
       {

//      Serial.print(t[j],15);
//     Serial.println("");
//     delay(500);
       } 

//initialise S to 0
for (i = 0; i < TSIZE; ++i) //S[i] = 0;

//implement the for k=1:length(A)

    for (k = 0; i < ASIZE; ++k){
     //devectorise the S calculation
     for (i = 0; i < TSIZE; ++i){
         S[i] = S[i] + pow(10, A[k]/20) * sin(2*M_PI*forigin[k]*t[i]);
         Serial.print(k);
       Serial.println("");
       delay(500);
     //}

[Guillaume]

After pasting code, select all the code then press the {}Code button to format it appropriately.

for (i = 0; i < TSIZE; ++i) //S[i] = 0;

The allocation should not be commented. In particular, since the ; is commented I'm not sure what the scope of the loop is.

for (k = 0; i < ASIZE; ++k){

Well, this time it's your fault. It's not what I wrote. It must be k < ASIZE. As you've written it then yes, the k loop will only execute once since at the 2nd iteration i is TSIZE.