##4.Forecast Function
def pop_forecast(geog,sheet,int_coef,dom_coef,start_period,end_period):
    for i in range (start_period,end_period+1):
       ###Forecast International and Domestic Net Migration.
       if geog=='AB':
           sheet[str(i)]['Int_Net_Mig']=round(sumproduct(int_coef,[1,(sheet[str(i-1)][0]/Exog['CAN_Tot_Pop'][i-1]),
                                        (Exog['AB_Tot_Emp'][i-1]-Exog['AB_Tot_Emp'][i-2]),(Exog['Imm_Pol'][i])]),0) 
           sheet[str(i)]['Dom_Net_Mig']=round(sumproduct(dom_coef,[1,sheet[str(i-1)]['Dom_Net_Mig'],(Exog['AB_Tot_UR'][i-1]
                                         /Exog['CAN_Tot_UR'][i-1]),0,(Exog['AB_Tot_Emp'][i-1]-Exog['AB_Tot_Emp'][i-2])]),0) 
       elif geog=='CER':
            sheet[str(i)]['Int_Net_Mig']=round(sumproduct(int_coef,[1,(AB[str(i)]['Int_Net_Mig']),(Exog['CER_Tot_UR'][i-1]/Exog['AB_Tot_UR'][i-1])]),0) #type: ignore
            sheet[str(i)]['Dom_Net_Mig']=round(sumproduct(dom_coef,[1,((AB[str(i)]['Dom_Net_Mig'])),(Exog['CER_Tot_UR'][i-1]/Exog['AB_Tot_UR'][i-1])]),0) #type: ignore
        
       elif geog=='CMA':
           sheet[str(i)]['Int_Net_Mig']=round(sumproduct(int_coef,[1, (CER[str(i)]['Int_Net_Mig'])]),0) #type: ignore
           sheet[str(i)]['Dom_Net_Mig']=round(sumproduct(dom_coef,[1, (CER[str(i)]['Dom_Net_Mig'])]),0) #type: ignore
       
       elif geog=='COC':
           sheet[str(i)]['Int_Net_Mig']=(sumproduct(int_coef,[1,(Exog['CER_Tot_UR'][i-1]/Exog['CAN_Tot_UR'][i-1]), (sheet[str(i-1)][0]/Exog['CAN_Tot_Pop'][i-1]),(Exog
                                        ['CER_Tot_Emp'][i-1]-Exog['CER_Tot_Emp'][i-2]),(Exog['COC_Avg_Hprice'][i-1]),(Exog['CMA_CPI'][i-1]),(Exog['Imm_Pol'][i-1])]))
           sheet[str(i)]['Dom_Net_Mig']=0
        
       else:
           print('geography listed cannot be found!')
       
       #Apply Alberta YTD Assumptions To First Forecast Period
       if i==start_period and geog=='AB':    
        sheet[str(start_period)]['Int_Net_Mig']=round(((1-(len(AB_YTD)*0.25))*sheet[str(start_period)]['Int_Net_Mig'])+sum(AB_YTD.Int_Net_Mig),0)
        sheet[str(start_period)]['Dom_Net_Mig']=round(((1-(len(AB_YTD)*0.25))*sheet[str(start_period)]['Dom_Net_Mig'])+sum(AB_YTD.Dom_Net_Mig),0)
       
       sheet[str(i)]['Tot_Net_Mig']=sheet[str(i)]['Int_Net_Mig']+sheet[str(i)]['Dom_Net_Mig'] 
       
       ###Shift Previous Age Cohorts A Year Ahead.
       sheet[str(i)][12:132]= sheet[str(i-1)][11:131]
       sheet[str(i)][133:253]=sheet[str(i-1)][132:252]

       ###Forecast Total Births By Gender as the Age Zero Cohort.
       sheet[str(i)]['m0']=round(globals()[geog + "_Birth"]['Ratio']['Male']*(sumproduct(np.array(globals()[geog + "_Fert"][i]),(sheet[str(i-1)][24:60]))),0)
       sheet[str(i)]['f0']=round(globals()[geog + "_Birth"]['Ratio']['Female']*(sumproduct(np.array(globals()[geog + "_Fert"][i]),(sheet[str(i-1)][24:60]))),0)
       sheet[str(i)]['Births']=sheet[str(i)]['m0']+sheet[str(i)]['f0']