#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#define MAX 200
float I[MAX],V[MAX], Imid[MAX], dIdV[MAX], lnI[MAX], I0, a, Vm;
float sumx, sumy, sumx2, sumxy,a,b;
int n,m;
FILE *fptr;
main(int argc, char *argv[]){
    if(argc !=2){
	printf("./analysis DATAFILE\n");
	exit(1);
    }
    fptr=fopen(argv[1], "r");
    m=0;
    do{
	fscanf(fptr, "%f %f", &V[m],&I[m]);
	m=m+1;
    }while(!feof(fptr));
    m=m-1;
    printf("\\begin{tabular}{|c|c|}\\hline\n");
    printf("{\\bf I (mA)} & {\\bf ${dI\\over dV}$ mA/V}\\\n\\hline\n");
    for(n=0;n<m-1;n++){
	Imid[n]=0.5*(I[n+1]+I[n]);
	dIdV[n]=(I[n+1]-I[n])/(V[n+1]-V[n]);
	printf("%f & %f\\\\\n", Imid[n], dIdV[n]);
    }
    printf("\\end{tabular}\n");

    /* compute slope and intercept of best fit */
    sumx=0.0, sumx2=0.0, sumy=0.0, sumxy=0.0;
    for(n=0;n<m-1;n++){
	sumx=sumx+Imid[n];
	sumx2=sumx2+Imid[n]*Imid[n];
	sumy=sumy+dIdV[n];
	sumxy=sumxy+dIdV[n]*Imid[n];
    }
    a=((float)(m-1)*sumxy-sumx*sumy)/((float)(m-1)*sumx2-sumx*sumx);
    b=(sumx2*sumy-sumx*sumxy)/((float)(m-1)*sumx2-sumx*sumx);
    I0=b/a;
    printf("$$dI/dV=%f+%f*I, \\qquad I_0=%f$$\n", b,a, I0);

 for(n=0;n<m;n++){
       lnI[n]=log(I[n]/I0+1.0);
   }
    printf("\n\n\\begin{tabular}{|c|c|}\\hline\n");
    printf("{\\bf V (V)} & {\\bf $\\ln({I\\over I_0}+1)$\\\n\\hline\n");
  for(n=0;n<m;n++){
	printf("%f & %f\\\\\n", V[n], lnI[n]);
    }
    printf("\\end{tabular}\n\n");
  

  /* compute slope and intercept of best fit */
    sumx=0.0, sumx2=0.0, sumy=0.0, sumxy=0.0;
    for(n=0;n<m;n++){
	sumx=sumx+V[n];
	sumx2=sumx2+V[n]*V[n];
	sumy=sumy+lnI[n];
	sumxy=sumxy+lnI[n]*V[n];
    }
    a=((float)(m)*sumxy-sumx*sumy)/((float)(m)*sumx2-sumx*sumx);
    b=(sumx2*sumy-sumx*sumxy)/((float)(m)*sumx2-sumx*sumx);

    printf("$$ln(I/%f+1)=%f+%f*V, \\qquad V_{min}=%f$$\n", I0, b,a, -b/a);

}