diff --git a/simulation_TREPR.m b/simulation_TREPR.m
index b052389..16f1189 100644
--- a/simulation_TREPR.m
+++ b/simulation_TREPR.m
@@ -1,7 +1,296 @@
-function [outputArg1,outputArg2] = simulation_TREPR(inputArg1,inputArg2)
+function [params] = simulation_TREPR(Exp,Sys,params)
 %SIMULATION_TREPR Summary of this function goes here
+%
 %   Detailed explanation goes here
-outputArg1 = inputArg1;
-outputArg2 = inputArg2;
+
+%% creating UI
+fig = figure;
+fig.Name = 'Simulation';
+fig.Units = 'Normalized';
+fig.Position = [.15 .2 .7 .6];
+fig.Tag = 'Normalize';
+
+%panel for plot
+plotpanel = uipanel(fig);
+plotpanel.Units = 'Normalized';
+plotpanel.Position = [.01 .01 .7 .98];
+%axes for plot
+ax = axes(plotpanel);
+ax.XLabel.String = 'magnetic field';
+ax.YLabel.String = 'Intensity';
+%plot manual simulation
+[bfield,spec] = pepper(Sys,Exp);
+spec_norm = spec/max(spec); % normalize the simulation
+plot(ax,0.1*params.Field_Vector,params.max_mean,'r',...
+     bfield,spec_norm,'b','LineWidth',1.2)
+legend('experimental','simulation')
+axis tight
+
+%% create push buttons
+s = uicontrol(fig,'Style','pushbutton');
+s.String = 'Start Fit';
+s.Units = 'Normalized';
+s.Position = [.72 .13 .27 .05];
+s.FontUnits = 'Normalized';
+s.FontSize = 0.6;
+s.Tag = 'Start';
+s.Callback = @SimStartButtonPushed;
+
+p = uicontrol(fig,'Style','pushbutton');
+p.String = 'Save Parameters';
+p.Units = 'Normalized';
+p.Position = [.72 .07 .27 .05];
+p.FontUnits = 'Normalized';
+p.FontSize = 0.6;
+p.Tag = 'Save';
+p.Callback = @SimSaveButtonPushed;
+
+d = uicontrol(fig,'Style','pushbutton');
+d.String = 'Done';
+d.Units = 'Normalized';
+d.Position = [.72 .01 .27 .05];
+d.FontUnits = 'Normalized';
+d.FontSize = 0.6;
+d.Tag = 'Done';
+d.Callback = @SimDoneButtonPushed;
+
+%% create input and text fields (Triplet)
+textTrip = uicontrol(fig,'Style','text');
+textTrip.String = 'Triplett population variations';
+textTrip.Units = 'Normalized';
+textTrip.Position = [.71 .94 .28 .05];
+textTrip.HorizontalAlignment = 'center';
+textTrip.FontUnits = 'Normalized';
+textTrip.FontSize = 0.6;
+textTrip.FontWeight = 'bold';
+textTrip.Tag = 'textTrip';
+
+textTx = uicontrol(fig,'Style','text');
+textTx.String = 'T_1 = ';
+textTx.Units = 'Normalized';
+textTx.Position = [.71 .89 .04333 .05];
+textTx.HorizontalAlignment = 'right';
+textTx.FontUnits = 'Normalized';
+textTx.FontSize = 0.6;
+textTx.Tag = 'textTx';
+
+InpTx = uicontrol(fig,'Style','edit');
+InpTx.String = '0';
+InpTx.Units = 'Normalized';
+InpTx.Position = [.75334 .89 .04333 .05];
+InpTx.HorizontalAlignment = 'left';
+InpTx.FontUnits = 'Normalized';
+InpTx.FontSize = 0.6;
+InpTx.Tag = 'InpTx';
+
+textTy = uicontrol(fig,'Style','text');
+textTy.String = 'T_2 = ';
+textTy.Units = 'Normalized';
+textTy.Position = [.80668 .89 .04333 .05];
+textTy.HorizontalAlignment = 'right';
+textTy.FontUnits = 'Normalized';
+textTy.FontSize = 0.6;
+textTy.Tag = 'textTy';
+
+InpTy = uicontrol(fig,'Style','edit');
+InpTy.String = '0';
+InpTy.Units = 'Normalized';
+InpTy.Position = [.85001 .89 .04333 .05];
+InpTy.HorizontalAlignment = 'left';
+InpTy.FontUnits = 'Normalized';
+InpTy.FontSize = 0.6;
+InpTy.Tag = 'InpTy';
+
+textTz = uicontrol(fig,'Style','text');
+textTz.String = 'T_3 = ';
+textTz.Units = 'Normalized';
+textTz.Position = [.90334 .89 .04333 .05];
+textTz.HorizontalAlignment = 'right';
+textTz.FontUnits = 'Normalized';
+textTz.FontSize = 0.6;
+textTz.Tag = 'textTz';
+
+InpTz = uicontrol(fig,'Style','edit');
+InpTz.String = '0';
+InpTz.Units = 'Normalized';
+InpTz.Position = [.94667 .89 .04333 .05];
+InpTz.HorizontalAlignment = 'left';
+InpTz.FontUnits = 'Normalized';
+InpTz.FontSize = 0.6;
+InpTz.Tag = 'InpTz';
+
+%% create input and text fields (D & E)
+textDE = uicontrol(fig,'Style','text');
+textDE.String = 'D tensor variation';
+textDE.Units = 'Normalized';
+textDE.Position = [.71 .78 .28 .05];
+textDE.HorizontalAlignment = 'center';
+textDE.FontUnits = 'Normalized';
+textDE.FontSize = 0.6;
+textDE.FontWeight = 'bold';
+textDE.Tag = 'textDE';
+
+textD = uicontrol(fig,'Style','text');
+textD.String = 'D = ';
+textD.Units = 'Normalized';
+textD.Position = [.71 .73 .0675 .05];
+textD.HorizontalAlignment = 'right';
+textD.FontUnits = 'Normalized';
+textD.FontSize = 0.6;
+textD.Tag = 'textD';
+
+InpD = uicontrol(fig,'Style','edit');
+InpD.String = '100';
+InpD.Units = 'Normalized';
+InpD.Position = [.7775 .73 .0675 .05];
+InpD.HorizontalAlignment = 'left';
+InpD.FontUnits = 'Normalized';
+InpD.FontSize = 0.6;
+InpD.Tag = 'InpD';
+
+textE = uicontrol(fig,'Style','text');
+textE.String = 'E = ';
+textE.Units = 'Normalized';
+textE.Position = [.855 .73 .0675 .05];
+textE.HorizontalAlignment = 'right';
+textE.FontUnits = 'Normalized';
+textE.FontSize = 0.6;
+textE.Tag = 'textE';
+
+InpE = uicontrol(fig,'Style','edit');
+InpE.String = '20';
+InpE.Units = 'Normalized';
+InpE.Position = [.9225 .73 .0675 .05];
+InpE.HorizontalAlignment = 'left';
+InpE.FontUnits = 'Normalized';
+InpE.FontSize = 0.6;
+InpE.Tag = 'InpE';
+
+%% create input and text fields (linewidth)
+textLW = uicontrol(fig,'Style','text');
+textLW.String = 'Linewidth variations';
+textLW.Units = 'Normalized';
+textLW.Position = [.71 .62 .28 .05];
+textLW.HorizontalAlignment = 'center';
+textLW.FontUnits = 'Normalized';
+textLW.FontSize = 0.6;
+textLW.FontWeight = 'bold';
+textLW.Tag = 'textLW';
+
+textGauss = uicontrol(fig,'Style','text');
+textGauss.String = 'lw(Gau) = ';
+textGauss.Units = 'Normalized';
+textGauss.Position = [.71 .57 .0675 .05];
+textGauss.HorizontalAlignment = 'right';
+textGauss.FontUnits = 'Normalized';
+textGauss.FontSize = 0.6;
+textGauss.Tag = 'textGauss';
+
+InpGauss = uicontrol(fig,'Style','edit');
+InpGauss.String = '1';
+InpGauss.Units = 'Normalized';
+InpGauss.Position = [.7775 .57 .0675 .05];
+InpGauss.HorizontalAlignment = 'left';
+InpGauss.FontUnits = 'Normalized';
+InpGauss.FontSize = 0.6;
+InpGauss.Tag = 'InpGauss';
+
+textLor = uicontrol(fig,'Style','text');
+textLor.String = 'lw(Lor) = ';
+textLor.Units = 'Normalized';
+textLor.Position = [.855 .57 .0675 .05];
+textLor.HorizontalAlignment = 'right';
+textLor.FontUnits = 'Normalized';
+textLor.FontSize = 0.6;
+textLor.Tag = 'textLor';
+
+InpLor = uicontrol(fig,'Style','edit');
+InpLor.String = '0';
+InpLor.Units = 'Normalized';
+InpLor.Position = [.9225 .57 .0675 .05];
+InpLor.HorizontalAlignment = 'left';
+InpLor.FontUnits = 'Normalized';
+InpLor.FontSize = 0.6;
+InpLor.Tag = 'InpLor';
+
+%% create input and text fields (g)
+textG = uicontrol(fig,'Style','text');
+textG.String = 'g-value variation = ';
+textG.Units = 'Normalized';
+textG.Position = [.71 .46 .2 .05];
+textG.HorizontalAlignment = 'right';
+textG.FontUnits = 'Normalized';
+textG.FontSize = 0.6;
+textG.Tag = 'textG';
+
+InpG = uicontrol(fig,'Style','edit');
+InpG.String = '0.01';
+InpG.Units = 'Normalized';
+InpG.Position = [.9225 .46 .0675 .05];
+InpG.HorizontalAlignment = 'left';
+InpG.FontUnits = 'Normalized';
+InpG.FontSize = 0.6;
+InpG.Tag = 'InpG';
+
+%% create input and text fields (FitOpt)
+textOpt = uicontrol(fig,'Style','text');
+textOpt.String = 'Fitting Options';
+textOpt.Units = 'Normalized';
+textOpt.Position = [.71 .35 .28 .05];
+textOpt.HorizontalAlignment = 'center';
+textOpt.FontUnits = 'Normalized';
+textOpt.FontSize = 0.6;
+textOpt.FontWeight = 'bold';
+textOpt.Tag = 'textFitOpt';
+
+textMeth = uicontrol(fig,'Style','text');
+textMeth.String = 'Method: ';
+textMeth.Units = 'Normalized';
+textMeth.Position = [.71 .30 .0675 .05];
+textMeth.HorizontalAlignment = 'right';
+textMeth.FontUnits = 'Normalized';
+textMeth.FontSize = 0.6;
+textMeth.Tag = 'textMeth';
+
+InpMeth = uicontrol(fig,'Style','edit');
+InpMeth.String = 'simplex fcn';
+InpMeth.Units = 'Normalized';
+InpMeth.Position = [.7775 .30 .2125 .05];
+InpMeth.HorizontalAlignment = 'left';
+InpMeth.FontUnits = 'Normalized';
+InpMeth.FontSize = 0.6;
+InpMeth.Tag = 'InpMeth';
+
+textScal = uicontrol(fig,'Style','text');
+textScal.String = 'Scaling: ';
+textScal.Units = 'Normalized';
+textScal.Position = [.71 .24 .0675 .05];
+textScal.HorizontalAlignment = 'right';
+textScal.FontUnits = 'Normalized';
+textScal.FontSize = 0.6;
+textScal.Tag = 'textScal';
+
+InpScal = uicontrol(fig,'Style','edit');
+InpScal.String = 'lsq';
+InpScal.Units = 'Normalized';
+InpScal.Position = [.7775 .24 .2125 .05];
+InpScal.HorizontalAlignment = 'left';
+InpScal.FontUnits = 'Normalized';
+InpScal.FontSize = 0.6;
+InpScal.Tag = 'InpScal';
+
+%% UI wait
+uicontrol(InpTx); %passes focus to first input
+uiwait(fig)
+
+%% Callback functions
+    function SimStartButtonPushed(src,event)
+        
+    end
+    
+    function SimDoneButtonPushed(src,event)
+        close 'Simulation'
+    end
+
 end