/
spm_diff.m
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spm_diff.m
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function [varargout] = spm_diff(varargin)
% matrix high-order numerical differentiation
% FORMAT [dfdx] = spm_diff(f,x,...,n)
% FORMAT [dfdx] = spm_diff(f,x,...,n,V)
% FORMAT [dfdx] = spm_diff(f,x,...,n,'q')
%
% f - [inline] function f(x{1},...)
% x - input argument[s]
% n - arguments to differentiate w.r.t.
%
% V - cell array of matrices that allow for differentiation w.r.t.
% to a linear transformation of the parameters: i.e., returns
%
% df/dy{i}; x = V{i}y{i}; V = dx(i)/dy(i)
%
% q - flag to preclude default concatenation of dfdx
%
% dfdx - df/dx{i} ; n = i
% dfdx{p}...{q} - df/dx{i}dx{j}(q)...dx{k}(p) ; n = [i j ... k]
%
%
% - a cunning recursive routine
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging
% Karl Friston
% $Id: spm_diff.m 4060 2010-09-01 17:17:36Z karl $
% create inline object
%--------------------------------------------------------------------------
f = varargin{1};
% parse input arguments
%--------------------------------------------------------------------------
if iscell(varargin{end})
x = varargin(2:(end - 2));
n = varargin{end - 1};
V = varargin{end};
q = 1;
elseif isnumeric(varargin{end})
x = varargin(2:(end - 1));
n = varargin{end};
V = cell(1,length(x));
q = 1;
elseif ischar(varargin{end})
x = varargin(2:(end - 2));
n = varargin{end - 1};
V = cell(1,length(x));
q = 0;
else
error('improper call')
end
% check transform matrices V = dxdy
%--------------------------------------------------------------------------
for i = 1:length(x)
try
V{i};
catch
V{i} = [];
end
if isempty(V{i}) && any(n == i);
V{i} = speye(length(spm_vec(x{i})));
end
end
% initialise
%--------------------------------------------------------------------------
m = n(end);
xm = spm_vec(x{m});
dx = exp(-8);
J = cell(1,size(V{m},2));
% proceed to derivatives
%==========================================================================
if length(n) == 1
% dfdx
%----------------------------------------------------------------------
f0 = feval(f,x{:});
for i = 1:length(J)
xi = x;
xmi = xm + V{m}(:,i)*dx;
xi{m} = spm_unvec(xmi,x{m});
fi = feval(f,xi{:});
J{i} = spm_dfdx(fi,f0,dx);
end
% return numeric array for first-order derivatives
%======================================================================
% vectorise f
%----------------------------------------------------------------------
f = spm_vec(f0);
% if there are no arguments to differentiate w.r.t. ...
%----------------------------------------------------------------------
if isempty(xm)
J = sparse(length(f),0);
% or there are no arguments to differentiate
%----------------------------------------------------------------------
elseif isempty(f)
J = sparse(0,length(xm));
end
% or differentiation of a vector
%----------------------------------------------------------------------
if isvec(f0) && q
% concatenate into a matrix
%------------------------------------------------------------------
if size(f0,2) == 1
J = spm_cat(J);
else
J = spm_cat(J')';
end
end
% assign output argument and return
%----------------------------------------------------------------------
varargout{1} = J;
varargout{2} = f0;
else
% dfdxdxdx....
%----------------------------------------------------------------------
f0 = cell(1,length(n));
[f0{:}] = spm_diff(f,x{:},n(1:end - 1),V);
for i = 1:length(J)
xi = x;
xmi = xm + V{m}(:,i)*dx;
xi{m} = spm_unvec(xmi,x{m});
fi = spm_diff(f,xi{:},n(1:end - 1),V);
J{i} = spm_dfdx(fi,f0{1},dx);
end
varargout = [{J} f0];
end
function dfdx = spm_dfdx(f,f0,dx)
% cell subtraction
%--------------------------------------------------------------------------
if iscell(f)
dfdx = f;
for i = 1:length(f(:))
dfdx{i} = spm_dfdx(f{i},f0{i},dx);
end
elseif isstruct(f)
dfdx = (spm_vec(f) - spm_vec(f0))/dx;
else
dfdx = (f - f0)/dx;
end
function is = isvec(v)
% isvector(v) returns true if v is 1-by-n or n-by-1 where n>=0
%__________________________________________________________________________
% vec if just two dimensions, and one (or both) unity
%--------------------------------------------------------------------------
is = length(size(v)) == 2 && isnumeric(v);
is = is && (size(v,1) == 1 || size(v,2) == 1);