# Copyright 2025, Gurobi Optimization, LLC## This example reads an LP model from a file and solves it.# If the model can be solved, then it finds the smallest positive variable,# sets its upper bound to zero, and resultolves the model two ways:# first with an advanced start, then without an advanced start# (i.e. 'from scratch').library(Matrix)library(gurobi)args<-commandArgs(trailingOnly=TRUE)if(length(args)<1){stop('Usage: Rscript lpmod.R filename\n')}# Read modelcat('Reading model',args[1],'...')model<-gurobi_read(args[1])cat('... done\n')# Determine whether it is an LPif('multiobj'%in%names(model)||'sos'%in%names(model)||'pwlobj'%in%names(model)||'cones'%in%names(model)||'quadcon'%in%names(model)||'genconstr'%in%names(model)){stop('The model is not a linear program\n')}# Detect set of non-continuous variablesintvars<-which(model$vtype!='C')numintvars<-length(intvars)if(numintvars>0){stop('problem is a MIP, nothing to do\n')}# Optimizeresult<-gurobi(model)if(result$status!='OPTIMAL'){cat('This model cannot be solved because its optimization status is',result$status,'\n')stop('Stop now\n')}# Recover number of variables in modelnumvars<-ncol(model$A)# Ensure bounds array is initializedif(is.null(model$lb)){model$lb<-rep(0,numvars)}if(is.null(model$ub)){model$ub<-rep(Inf,numvars)}# Find smallest (non-zero) variable value with zero lower boundx<-replace(result$x,result$x<1e-4,Inf)x<-replace(x,model$lb>1e-6,Inf)minVar<-which.min(x)minVal<-x[minVar]# Get variable namevarname<-''if(is.null(model$varnames)){varname<-sprintf('C%d',minVar)}else{varname<-model$varnames[minVar]}cat('\n*** Setting',varname,'from',minVal,'to zero ***\n\n')model$ub[minVar]<-0# Set advance start basis informationmodel$vbasis<-result$vbasismodel$cbasis<-result$cbasisresult2<-gurobi(model)warmCount<-result2$itercountwarmTime<-result2$runtime# Reset-advance start informationmodel$vbasis<-NULLmodel$cbasis<-NULLresult2<-gurobi(model)coldCount<-result2$itercountcoldTime<-result2$runtimecat('\n*** Warm start:',warmCount,'iterations,',warmTime,'seconds\n')cat('\n*** Cold start:',coldCount,'iterations,',coldTime,'seconds\n')# Clear spacerm(model,result,result2)