function planck=planck(wavenum,temp)

% PLANCK(wavenum,temp) computes the planck or blackbody radiance of a body 
% given its radiating temperature(K) and the wavenumber(cm-1) of radiation.
%
% If WAVENUM and TEMP are column and row vectors, respectively, then PLANCK
% will return the corresponding matrix (n_v .* n_T) of planck function values.
% It does so according to the formula B(v,T)=2h*c^2*v^3/(exp(hcv/kT)-1)
% The constants 2hc^2 and hc/kT have 7 significant digits of precision
%
% WAVENUM is the wavenumber of radiation (ROW vector) (cm-1)
% TEMP    is the radiating temperature of the blackbody (COLUMN vector) (K)
%
% (C) Ben Quine, University of Toronto, 07-SEP-1999.

% Modifications: L.Buckley 2-JUN-1999 to make output matrix size compatible with RADIANCE2
%					  B.Quine 7-SEP-1999 rewritten to accept matrix computations

%Define Constants
c1=1.191062e-8; %2hc^2
c2=1.438786;    %hc/kT

if size(wavenum,2)~=1 
   error('GENSPECT PLANCK: Wavenumber input must be a column vector')
end
if size(temp,1)~=1
   error('GENSPECT PLANCK: Temperature input must be a row vector')
end

% Do matrix calculation
planck=((c1.*(wavenum.^3))*ones(size(temp)))./(exp(wavenum*(c2./temp))-1);