diff --git a/source/IO/FORCING/FORCING_ubT_lbT_fixed.m b/source/IO/FORCING/FORCING_ubT_lbT_fixed.m
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+%========================================================================
+% CryoGrid FORCING class FORCING_ubT_lbT_fixed
+% simple model forcing for GROUND classes depending only on fixed upper
+% and lower boundary temperatures
+%
+% The mandatory userdefined parameters are:
+% start_time
+% end_time
+% time_step
+% T_ub   Upper boundary temperature.
+% T_lb   Lower boundary temperature.
+%
+% T. Ingeman-Nielsen, December 2021
+%========================================================================
+
+
+classdef FORCING_ubT_lbT_fixed < matlab.mixin.Copyable
+    
+    properties
+        forcing_index
+        DATA            % forcing data time series
+        TEMP            % forcing data interpolated to a timestep
+        PARA            % parameters
+        STATUS         
+        CONST         
+    end
+    
+    
+    methods
+
+        function forcing = provide_PARA(forcing)         
+            % INITIALIZE_PARA  Initializes PARA structure, setting the variables in PARA.  
+
+            forcing.PARA.start_time = [];     % start time of the simulations (must be within the range of data in forcing file)
+            forcing.PARA.end_time = [];       % end time of the simulations (must be within the range of data in forcing file)
+            forcing.PARA.time_step = [];      % time step of timeseries [days] (e.g. 0.5 days)
+            forcing.PARA.T_ub = [];           % 
+            forcing.PARA.T_lb = [];           % 
+        end
+        
+        function forcing = provide_CONST(forcing)
+            
+        end
+        
+        function forcing = provide_STATVAR(forcing)
+            
+        end
+        
+        function forcing = initialize_excel(forcing)
+            
+        end
+ 
+        
+        function forcing = finalize_init(forcing, tile)
+            % FINALIZE_INIT  Performs all additional property
+            %   initializations and modifications. Checks for some (but not
+            %   all) data validity.
+            
+            forcing.STATUS = 1;
+
+            % handle start time
+            forcing.PARA.start_time = datenum(forcing.PARA.start_time(1,1), forcing.PARA.start_time(2,1), forcing.PARA.start_time(3,1));
+            
+            % handle end time
+            forcing.PARA.end_time = datenum(forcing.PARA.end_time(1,1), forcing.PARA.end_time(2,1),forcing.PARA.end_time(3,1));
+
+            % generate time sequence
+            forcing.DATA.timeForcing = forcing.PARA.start_time:forcing.PARA.time_step:forcing.PARA.end_time;
+            forcing.PARA.time_zero = datenum(datetime(year(datetime(forcing.PARA.start_time,'ConvertFrom','datenum')),1,1,0,0,0));
+
+            %initialize TEMP
+            forcing.TEMP.snowfall=0;
+            forcing.TEMP.rainfall=0;
+            forcing.TEMP.Tair=0;
+            forcing.TEMP.T_ub=0;
+            forcing.TEMP.T_lb=0;
+            
+        end
+
+
+        function forcing = interpolate_forcing(forcing, tile)
+            % Interpolate forcing data to timestep tile.t
+            t = tile.t;
+            
+            forcing.TEMP.T_ub = forcing.PARA.T_ub;
+            forcing.TEMP.T_lb = forcing.PARA.T_lb;
+            forcing.TEMP.Tair = forcing.TEMP.T_ub;
+            forcing.TEMP.t = t;
+        end
+
+        function xls_out = write_excel(forcing)
+			% XLS_OUT  Is a cell array corresponding to the class-specific content of the parameter excel file (refer to function write_controlsheet).
+			error('This function is not implemented/updated for this specific class')
+            xls_out = {'FORCING','index',NaN,NaN;'FORCING_seb',1,NaN,NaN;NaN,NaN,NaN,NaN;'filename',NaN,NaN,NaN;'start_time',NaN,NaN,'provide in format dd.mm.yyyy; if left empty, the first timestamp of the forcing data set will be used';'end_time',NaN,NaN,'provide in format dd.mm.yyyy; if left empty, the last timestamp of the forcing data set will be used';'rain_fraction',1,'[-]','rainfall in forcing file multiplied by this number';'snow_fraction',1,'[-]','snowfall in forcing file multiplied by this number';'latitude',NaN,'[degree]','geographical coordinates';'longitude',NaN,'[degree]',NaN;'altitude',NaN,'[m]','a.s.l.';'domain_depth',100,'[m]','should match a GRID point, model domain extends to this depth';'heatFlux_lb',0.0500000000000000,'[W/m2]','geothermal heat flux';'airT_height',2,'[m]','height of air temperature';'FORCING_END',NaN,NaN,NaN};
+        end
+
+        function fig = plot(forcing)
+			error('This function is not implemented/updated for this specific class')
+        end
+
+    end
+
+    
+    methods(Static)
+        function value = lin_interp(t, posit, times, data)
+			% t       is the current time
+			% times   is the vector of times at which forcing data are available
+			% data    is the vector of forcing data (on parameter)
+			% posit   is an index into the time vector to the largest specified time step before current time 
+            value = data(posit,1) + (data(posit+1,1) - data(posit,1)).*(t-times(posit,1))./(times(2,1)-times(1,1));
+        end        
+    end
+    
+
+end
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