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# spikes

## (PublicToolbox/regutools/spikes.m in BrainStorm 2.0 (Alpha))

### Function Synopsis

[A,b,x] = spikes(n,t_max)

### Help Text

SPIKES Test problem with a "spiky" solution.
[A,b,x] = spikes(n,t_max)
Artificially generated discrete ill-posed problem.
The solution x consists of a unit step at t = .5, and a pulse train
of spikes of decrasing magnitude at t = .5, 1.5, 2.5, ...
The parameter t_max is optional; its default value is 5.
It controls the length of the pulse train.

### Listing of function C:\BrainStorm_2001\PublicToolbox\regutools\spikes.m

function [A,b,x] = spikes(n,t_max)
%SPIKES Test problem with a "spiky" solution.
%
% [A,b,x] = spikes(n,t_max)
%
% Artificially generated discrete ill-posed problem.
%
% The solution x consists of a unit step at t = .5, and a pulse train
% of spikes of decrasing magnitude at t = .5, 1.5, 2.5, ...
%
% The parameter t_max is optional; its default value is 5.
% It controls the length of the pulse train.
% Per Christian Hansen, UNI-C, 06/24/91.
% Initialization.
if (nargin == 1), t_max = 5; end
t = t_max*[1:n]/n; del = t_max/n;
% Compute the matrix A.
[t,sigma] = meshdom(del:del:t_max,del:del:t_max); sigma = flipud(sigma);
A = sigma./(2*sqrt(pi*t.^3)).*exp(-(sigma.^2)./(4*t));
% Compute the right-hand side b and the solution x.
if (nargout > 1)
heights = 2*ones(t_max,1); heights(1) = 25;
heights(2) = 9; heights(3) = 5; heights(4) = 4; heights(5) = 3;
x = zeros(n,1); n_h = 1;
peak = 0.5/t_max; peak_dist = 1/t_max;
if (peak < 1)
n_peak = round(peak*n); x(n_peak) = heights(n_h);
x(n_peak+1:n) = ones(n-n_peak,1);
peak = peak + peak_dist; n_h = n_h + 1;
end
while (peak < 1)
x(round(peak*n)) = heights(n_h);
peak = peak + peak_dist; n_h = n_h + 1;
end
b = A*x;
end

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