nick-example-ompr.R

library(dplyr)
library(ROI)
library(ROI.plugin.glpk)
library(ompr)
library(ompr.roi)

rb_mat <- function(r,c,prob) matrix(rbinom(r*c,1,prob),r,c)

my_A <- rb_mat(r = 1000, c = 200) # 1000 heart attacks, 200 potential locations

# number of OHCA incidents
J <- nrow(my_A)
I <- ncol(my_A)
# number of AEDs
N <- 5

MIPModel() %>%
    add_variable(x[j], j = 1:J, type = "binary") %>%
    add_variable(y[i], i = 1:I, type = "binary") %>%
    # add_variable(a[i,j], i = 1:I, j = 1:J, type = "binary") %>%
    add_variable(my_A[i,j], i = 1:I, j = 1:J, type = "binary") %>%
    set_objective(sum_exp(x[j], j = 1:J), "max") %>%
    add_constraint(sum_exp(y[i], i = 1:I), "==", N) %>%
    add_constraint(sum_exp(a[i,j] * y[i], i = 1:I, j = 1:J), ">=", x[j])

# > Error in on_element(push, inplace_update_ast, get_ast_value, element) : 
# > The expression contains a variable, that is not part of the model.

Hi @dirkschumacher,
Im trying to solve a problem on optimization .We have an list of 68 raw materials in inventory stock in a vector called Inv stock .And we have the required amount of items in an array qty_req. We have a matrix of raw materials which has list of raw materials as column and rows contains the quantity of raw material req to complete a unit of item per order. That means complete raw materials required to complete each order can be determined by multiplying the qty_req vector with the raw material matrix .

Problem: We want to find qtysold as a output which should give us the appropriate qty to be manufactured instead of qty req so that we complete atleast 80% of each order and the max revenue can be obtained. We have revenue/unit for each order .

Eg of Raw material matrix is as below:

OrderNo.	A	B	C
1	0	1	1
2	2	3	0
3	1	2	3

Eg. of req_qty vector

OrderNo.	Qty req
1	2
2	1
3	3

Eg. of Inv_stock

A	B	C
4	0	4

Eg of Revenue per unit

OrderNo.	Revenue/unit
1	2400
2	4500
3	450

Total material required for manufacturing the req quantity will become req_qty* Raw_material.

Please find below the code which is not working. Please provide your suggestions .
model <- MIPModel() %>%
add_variable(Qtysold[i],i=1:n,type = "integer" ,lb=0 ) %>%
add_variable(Total_mat[i,j],i=1:n,j=1:68, type = "continuous", lb = 0) %>%
set_objective(sum_expr(Qtysold[i]*Revenueperunit[i],i=1:n), "max")%>%
add_constraint(Qtysold[i] <= qty_req[i], i = 1:n)%>%
add_constraint(Qtysold[i]*Raw_mat==Total_mat[i,j],i=1:n,j=1:68)%>%
add_constraint(sum_expr(Total_mat[i,j],i=1:n)<=Inv_Stock[1,j],j=1:68)
result <- solve_model(model, with_ROI(solver = "glpk"))

On adding the last two lines im getting errors like unexpected operator '('.

Thanks in advance.

Hi @dirkschumacher, @njtierney,
I am solving an optimization problem using the followoing code.
library(Rglpk)
library(magrittr)
library(dplyr)
library(ROI)
library(ROI.plugin.glpk)
library(ompr)
library(ompr.roi)
data<-read.csv('input.csv',header=TRUE,sep=",")
Inv_Stock<-read.csv('INV_DATA.csv',header = TRUE,sep = ",")
Inv_Stock<- sapply(Inv_Stock,as.matrix)
qty_req<- data[,5]
qty_req<- sapply(qty_req,as.double)

Revenueperunit<-data[,4]
Revenueperunit<-sapply(Revenueperunit,as.double)

Raw_mat<-data[,-c(1,2,3,4,5)]
Raw_mat <- sapply(Raw_mat,as.matrix)

model <- MIPModel() %>%
add_variable(Qtysold[i],i=1:n,type = "integer" ,lb=0 ) %>%
add_variable(Total_mat[i,j],i=1:n,j=1:68, type = "continuous", lb = 0) %>%
set_objective(sum_expr(Qtysold[i]*Revenueperunit[i],i=1:n), "max")%>%
add_constraint(Qtysold[i] <= qty_req[i], i = 1:n)%>%
add_constraint(rawmat[j,i]*Qtysold[i]==Total_mat[j,i])%>%
add_constraint(sum_expr(Total_mat[i,j],i=1:n)<=Inv_Stock[1,j],j=1:68)
result <- solve_model(model, with_ROI(solver = "glpk"))

Context of the problem:
A vector holding inventory of total raw materials available by colums containing the raw material name and a single row with total qty available per column.
A matrix raw material with column names of raw material and each row indicating per order number, the quantity if raw material req for unit item to be manufactured.
A vector qty req indicating per order number the number of quantity asked by a customer to manufacture.
A vector revenue/unit indicating the revenue from each unit of material per order.
Problem statement:
We want to maximize total revenue
we want to determine qtysold such that atleast 80% of the qty req per order is delivered.
when we multiply qtysold with req raw material matrix , total req raw material columnwise should not exceed the total available in inventory stock.

Error: while adding last two constraints, its not giving answer, it says'(' unexpected operator found.
Error in acc[[key]] : no such index at level 1

Hi, I am now facing issue in only last line, can anyone please tell if this is making it a quadratic constraint.

model <- MIPModel() %>%
add_variable(Qtysold[i],i=1:n,type = "integer" ,lb=0 ) %>%
add_variable(Total_mat[i,j],i=1:n,j=1:68, type = "continuous", lb = 0) %>%
set_objective(sum_expr(Qtysold[i]*Revenueperunit[i],i=1:n), "max")%>%
add_constraint(Qtysold[i] <= qty_req[i], i = 1:n)%>%
add_constraint(Qtysold[i]*Raw_mat[i,j]==Total_mat[i,j],i=1:n,j=1:68)%>%
add_constraint(colSums(Total_mat[i,j],i=1:n)<=Inv_Stock[j],j=1:68)

Error:rror in check_for_unknown_vars_impl(model, the_ast) :
The expression contains a variable that is not part of the model.