% mexReadGrad: read gradient files into a matrix
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% Usage:
% gradMatrix = mexReadGrad(type, number)
% gradMatrix = mexReadGrad('grad.txt')
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% INPUT
% type : gradient type or gradient file name (.txt)
% 'elec': gradients from camino based on electrostatic energy.
% 'tess': gradients based on tessellation.
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% number : if type=='elec', then number means the number of samples.
% if type=='tess', then number means tessellation order.
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% OUTPUT
% grad : Nx3 matrix, each row is a point in sphere.
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% Copyright (c) 2013, Jian Cheng <jian.cheng.1983@gmail.com>
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