da2dm.m

% DA2DM  Convert the aerodynamic diameter to a mobility diameter. 
%  
%  DM = da2dm(DA,PROP) converts the aerodynamic diameter, DA, to a 
%  mobility diameter, DM, using the properties in PROP. 
%  
%  DM = da2dm(...,F_ITER) adds a flag indicating whether 
%  to use the simple (F_ITER = 0) or iterative (F_ITER = 1) 
%  evaluation. The former is less accurate but faster. Default is
%  F_SIMPLE = 1.
%  
%  ------------------------------------------------------------------------
%  
%  AUTHOR: Timothy Sipkens, 2022-01-27

function dm = da2dm(da, prop, f_iter, varargin)

%-- Parse inputs --------------------------%
if ~exist('f_iter', 'var'); f_iter = []; end
if isempty(f_iter); f_iter = 1; end
%------------------------------------------%

rho0 = 1e3;  % density of water

% Compute simple volume-equivalent and aerodynamic diameters, 
% that is without iteration. 
opts = optimset('Display', 'off');
fun = @(dm) 1e9 .* ...
    (dm .* 1e-9 .* sqrt(dm2rhoeff(dm .* 1e-9, prop) ./ rho0) - da);
dm = fsolve(fun, da .* 1e9, opts) .* 1e-9;

%-{
% Alternate, iterative method that is more precise.
if f_iter
    % Solve for mobility diameter. 
    fun = @(dm) 1e9 .* (dm .* 1e-9 .* ...
        sqrt(dm2rhoeff(dm .* 1e-9, prop) ./ rho0 .* ...
        Cc(dm .* 1e-9, varargin{:}) ./ Cc(da, varargin{:})) - da);
    dm = fsolve(fun, dm .* 1e9, opts) .* 1e-9;
end
%}

dm = real(dm);

end