drsc_linesearch

Line search subroutine to determine stepsize for gradient ascent performed by DRSC
STEP = DRSC_LINESEARCH(DATA, W, MAX_STEP, F, GRAD, SIGMA, U, DEGS)

Line-search for gradient ascent within DRSC satisfying only first Wolfe condition 
(using both takes excessively long)

 Inputs:
    (DATA): N-by-D data matris
    (W):     Projection matrix (ascent is performed w.r.t. last column of W)
    (MAX_STEP): Maximum stepszie    
    (F):    Function value at current poit
    (GRAD):    Gradient at current point
    (SIGMA): Scale parameter for Gaussian kernel (used to estimate similarity matrix)
    (U):    Top K eigenvectors of D^{-1/2} *K*D^{-1/2}
    (DEGS): Vector of degrees of each vertex: D = diag(degs)

 Output:
    (STEP): Stepsize satisfying 1st Wolfe condition
        (Returns 0 if no such stepsize is found)