function gains = interp_gain_c(field_patterns, angles, at_values, interp_method)%INTERP_GAIN_C Antenna field pattern interpolation (requires GSL)%   G = INTERP_GAIN_C(PAT, ANGLES, DATA, METHOD) are the%   complex antenna field patterns interpolated at azimuth angles given in DATA, %   given in degrees. SIZE(G)=[NUM_EL SIZE(DATA)], where NUM_EL is the %   number of rows in matrix PAT. PAT has LENGTH(ANGLES) columns; ANGLES %   is a vector defining the angles (in degrees) at which the antenna %   element patterns in the rows of PAT have been defined. Note: LENGTH(ANGLES)%   must equal SIZE(PAT,2), i.e. all field patterns have to be specified %   over the same azimuth grid. %   %   METHOD is a string defining interpolation method. The recommended methods%   are:%   'linear'        =   linear interpolation   %   'cspline'       =   cubic spline with periodic boundary conditions%   'nearest'       =   rounds to nearest known point%%   The default method is 'cspline'. Note that 'linear' cannot extrapolate%   values falling outside the support of the interpolated function and %   'nearest' requires that ANGLES is uniformly sampled in angular domain.%%   Usage of this function requires that interp_gain_mex.c is compiled. %   To compile, type %%       mex -lgsl -lgslcblas -lm interp_gain_mex.c %%   The compilation requires that GNU Scientific Library (GSL) is properly%   installed in your system and the mex compiler is able to use it.  %   %   It is recommended that the antenna field patterns in PAT are given %   so that there are no duplicate points in ANGLES and that the %   support of the interpolated function spans over the entire azimuth%   angle, i.e. 360 degrees. %%   Real and imaginary parts are interpolated separately. Elevation %   interpolation is not supported currently.%%   Ref.: http://www.gnu.org/software/gsl/%%   See also INTERP_GAIN. %   Authors: Jussi Salmi (HUT), Jari Salo (HUT)%   $Revision: 0.1 $  $Date: Aug 11, 2004$% field_pattern - complex field patterns of the antennas, SIZE()=[NUM_EL AZ_VALUES] % angles        - a vector with LENGTH(AZ_VALUES)% at_values     - an N-D array% gains         - interpolated complex gains, SIZE()=[NUM_EL SIZE(at_values)]if (size(field_patterns,2) ~= numel(angles))    error('Size mismatch in antenna parameters! ')endsiz_at_values    = size(at_values);nd               = ndims(at_values);num_elements     = size(field_patterns,1);tol = 1e-5; % tolerance to be added if dublicate angles exist% next lines sort the interpolation values in ascending order and % check if there are same values more than once.[angles I] = sort(angles);Id = 1;while (~isempty(Id))    y_diff = diff(angles);     Id = find(y_diff==0);    angles(Id) = angles(Id) - tol;end% check interpolation method% Additional methods are:% 'csplinenat'    =   cubic spline with natural boundary conditions% 'akima'         =   Non-rounded Akima spline with natural boundary conditions.% 'akimap'        =   Non-rounded Akima spline with periodic boundary conditions.if isequal(lower(interp_method),'linear')    type = 1;else    if isequal(lower(interp_method),'cspline')        type = 2;    else        if isequal(lower(interp_method),'nearest')            type = 3;        else            if isequal(lower(interp_method),'csplinenat')                type = 4;            else                if isequal(lower(interp_method),'akima')                    type = 5;                else                    if isequal(lower(interp_method),'akimap')                        type = 6;                    else                        type = 2; % default is 'cspline'                    end                end            end        end    endend        % interpolate real part values % extrapolate values outside the user-defined antenna pattern interp_real = interp_gain_mex(angles(:), real(field_patterns(:,I).'), at_values(:),type);if isreal(field_patterns) % check if fieldpatterns is real valued    gains = interp_real;    else    % fieldpatterns is complex        % Interpolate imaginary part. Note that interpolated values are in degrees    % extrapolate values outside the user-defined antenna pattern    interp_imag = interp_gain_mex(angles(:), imag(field_patterns(:,I).'), at_values(:),type);        % back to complex values, this has size [PROD(siz_at_values) num_elements]     gains=complex(interp_real,interp_imag);end% make the output size [num_elements siz_at_values]gains=reshape(gains,[siz_at_values num_elements]);gains=permute(gains,[nd+1 1:nd]);