calcSurrogateModel.m

% This function is part of the NMSM Pipeline, see file for full license.
%
% This function uses symbolic polynomial expressions to approximate 
% muscle tendon lengths and moment arms
%
% Inputs:
% params.polynomialExpressionMuscleTendonLengths (1 x numberOfMuscles)
% params.polyninomialExpressionMomentArms (1 x numberOfMuscles)
% params.coefficients (1 x numberOfMuscles)
% params.dofsActuated (numberOfCoordinates x numberOfMuscles)
% jointAngles (1 x numberOfMuscles)
%
% (Symbol cell array, Symbol cell array, Number cell array, 
% Number cell array) -> (2D Number array, Number cell array)
%
% returns estimated muscle tendon lengths and moment arms 

% -----------------------------------------------------------------------

function [newMuscleTendonLengths, newMomentArms, ...
    newMuscleTendonVelocities] = calcSurrogateModel(params, jointAngles, ...
    jointVelocities)

newMomentArms = zeros(size(jointAngles{1}, 1), ...
    length(params.coordinateNames), size(jointAngles, 2));
for i = 1 : size(jointAngles, 2)
    % Get A matrix
    matrix = PatientSpecificSurrogateModel(jointAngles{i}, jointVelocities{i}, i);
    % Caculate new muscle tendon lengths and moment arms
    vector = matrix * params.coefficients{i};
    newMuscleTendonLengths(:, i) = vector(1 : size(jointAngles{i}, 1));
    newMuscleTendonVelocities(:, i) = vector(1 + ...
        size(jointAngles{i}, 1) : size(jointAngles{i}, 1) * 2);
    index = 2;
    for j = 1 : length(params.coordinateNames)
        for k = 1 : length(params.surrogateModelLabels{i})
            if strcmp(params.coordinateNames(j), params.surrogateModelLabels{i}(k))
                newMomentArms(:, j, i) = vector(size(jointAngles{i}, 1) * ...
                    index + 1 : size(jointAngles{i}, 1) * (index + 1));
                index = index + 1;
            end
        end
    end
end
end