how to find area under the curve ?

Answer 1

[John D'Errico]

Easy. Just use trapz.

help trapz

 TRAPZ  Trapezoidal numerical integration.
    Z = TRAPZ(Y) computes an approximation of the integral of Y via
    the trapezoidal method (with unit spacing).  To compute the integral
    for spacing different from one, multiply Z by the spacing increment.
 
    For vectors, TRAPZ(Y) is the integral of Y. For matrices, TRAPZ(Y)
    is a row vector with the integral over each column. For N-D
    arrays, TRAPZ(Y) works across the first non-singleton dimension.
 
    Z = TRAPZ(X,Y) computes the integral of Y with respect to X using the
    trapezoidal method. X can be a scalar or a vector with the same length
    as the first non-singleton dimension in Y. TRAPZ operates along this
    dimension. If X is scalar, then TRAPZ(X,Y) is equivalent to X*TRAPZ(Y).
 
    Z = TRAPZ(X,Y,DIM) or TRAPZ(Y,DIM) integrates across dimension DIM
    of Y. The length of X must be the same as size(Y,DIM)).
 
    Example:
        Y = [0 1 2; 3 4 5]
        trapz(Y,1)
        trapz(Y,2)
 
    Class support for inputs X, Y:
       float: double, single
 
    See also SUM, CUMSUM, CUMTRAPZ, INTEGRAL.

    Documentation for trapz
       doc trapz

    Other functions named trapz

       codistributed/trapz    gpuArray/trapz

Answer 2

[SALAH ALRABEEI]

Use polyarea(x,y); you need to have a polygon; That is, ur first point must by ur lasr point. You can do so by adding this to ur x y data x(end+1)=x(1);y(end+1)=y(1);

Then apply the polyarea function

See here