C – From Matlab To C – Some useful functions

Here are 3 basics functions that can be useful if you are translating matlab functions to C language.

The Functions

We translate this functions into C. Some of this functions use variables number of arguments.
In this case, this is generally like func(NB_ARG, [ARGS]);. Please, be very careful to put the arguments in double and not in integer! For example, do not use “2″ but “2.0″.

// Matlab B = 88 * ones(50,1)
double* B = instance(50, 88.0);

// Matlab C = [1 1 2 2 3 3]
double* C = vectorize(6, 1.0 , 1.0 , 2.0 , 2.0 , 3.0 , 3.0);

// Matlab D = [0.1,0.1,0.1, 0.3,0.3, 0.9,0.9,0.9]
double* D = multiinstance(7,3, 3,0.1, 2,0.3, 3,0.9);

// Matlab E = [start;step;end]
double* E = createTab(start, step, end);

// Matlab Titem = interp1(dt1,dt2,dt3,'linear');
double* Titem = interp1(dt1,sizedt1,dt2,dt3,sizedt3);

In C

/** To inter-pole data */
double* interp1(double * x, int sizex, double * y , double * xi, int sizexi){
	// indexes
	int idyi = 0;
	int idx = 0;
	// After computing, to know the current step progress
	double steps = (y[1] - y[0]) / (x[1] - x[0]);

	// fill left points
	while(idyi < sizexi - 1 && xi[idyi] < x[0]){
		yi[idyi] = y[0] - (steps * (x[0] - xi[idyi]) ) ;
		++idyi;
	}

	// fill point in the same interval as the original values
	while(idyi < sizexi && idx < sizex){
		while(idx < sizex && xi[idyi] >= x[idx]){
			++idx;
		}
		if(idx != sizex){
			steps = (y[idx] - y[idx-1]) / (x[idx] - x[idx-1]);
			yi[idyi] = y[idx] - (steps * (x[idx] - xi[idyi]) ) ;
			++idyi;
		}
	}

	// fill the right points
	if(idyi < sizexi){
		steps = (y[sizex - 1] - y[sizex-2]) / (x[sizex-1] - x[sizex-2]);
		while(idyi < sizexi){
			yi[idyi] = y[sizex-1] + (steps * (xi[idyi] - x[sizex-1])) ;
			++idyi;
		}
	}

	return yi;
}

/** Create a tab like matlab [start;step;end] */
double* createTab(double start, double step, double end){
	// Size
	int size = 1 + fabs((end - start)/step);
	// Alloc
	double * tab = (double*)malloc(sizeof(double) * size);
	// Fill
	for(int idx = 0; start <= end && idx < size; start += step, ++idx){
		tab[idx] = start;
	}
	return tab;
}

/** Create a tab with a value in all cases */
double* instance(int size, double val){
	// Alloc
	double * tab = (double*)malloc(sizeof(double) * size);
	// Fill
	while(size--){
		tab[size] = val;
	}
	return tab;
}

/** Multi Parameter Tab */
/** PUT VALUES IN DOUBLE! */
/** ex : multiinstance(7,3, 3,0.1, 2,0.3, 3,0.9) => [0.1,0.1,0.1, 0.3,0.3, 0.9,0.9,0.9] */
double* multiinstance( int totalsize, int seriesSize, ... )
{
	// Variables arguments Input
	va_list arguments;
	// Alloc
	double *tab = (double*)malloc(sizeof(double) * totalsize);

	int idx = 0, step = 0;
	double value = 0.0;

	// Start Using arguments
	va_start ( arguments, seriesSize );

	// From 0 to totalSize
	for(idx = 0 ; idx < totalsize ; ++idx, --step){
		// Cycle?
		if(step == 0){
			// Get new step & value
			step = va_arg ( arguments, int );
			value = va_arg ( arguments, double );
		}
		// Fill
		tab[idx] = value;
	}

	va_end ( arguments );

	return tab;
}

/** Create a vector from value */
/** PUT VALUES IN DOUBLE! */
/** ex : vectorize(2.0,0.0,5.0) => [0,5] */
double* vectorize( int size, ... )
{
	// Variables Arguments
	va_list arguments;
	double *tab = (double*)malloc(sizeof(double) * size);

	//Use argument
	va_start ( arguments, size );

	for(int idx = 0 ; idx < size ; ++idx){
		tab[idx] = va_arg ( arguments, double );
	}

	va_end ( arguments );

	return tab;
}

This functions are given “as is” without any warranty.
Please, put the post URL in your program to say where you find the code.