# Curve Fitting y = ab^x Using C++ with Output

C++ Program for fitting curve y=abx using least square method with output.

## C++ Program for Fitting y = abx

``````
#include<iostream>
#include<math.h>

#define S 50

using namespace std;

int main()
{
int n, i;
float x[S], y[S], sumX=0, sumX2=0, sumY=0, sumXY=0, a, b, A, B;

/* Input */
cout<<"How many data points? " << endl;
cin >> n;

for(i=1;i<=n;i++)
{
cout << "x["<< i <<"] = ";
cin >> x[i];
cout << "y["<< i <<"] = ";
cin >> y[i];
}

/* Calculating Required Sum */
for(i=1;i<=n;i++)
{
sumX = sumX + x[i];
sumX2 = sumX2 + x[i]*x[i];
sumY = sumY + log(y[i]);
sumXY = sumXY + x[i]*log(y[i]);
}

/* Calculating A and B */
B = (n*sumXY-sumX*sumY)/(n*sumX2-sumX*sumX);
A = (sumY - B*sumX)/n;

/* Transformation of A to a and B to b */
a = exp(A);
b = exp(B);

/* Displaying value of a and b */
cout << "Values are: a = " << a << " and b = " << b;

return(0);
}

``````

## Output

```
How many data points?
5
x = 0
y = 3
x = 1
y = 6
x = 2
y = 12
x = 3
y = 24
x = 4
y = 48
Values are: a = 3 and b = 2

```