fix modify and tests

Author: rafabench

src/MOI_wrapper/MOI_wrapper.jl

@@ -2166,17 +2166,23 @@ function MOI.modify(
     cols = Vector{Cint}(undef, nels)
     coefs = Vector{Cdouble}(undef, nels)
     for i in 1:nels
-        row = Cint(_info(model, cis[i]).row)
-        col = column(model, changes[i].variable)
+        rows[i] = Cint(_info(model, cis[i]).row)
+        cols[i] = column(model, changes[i].variable)
+        coefs[i] = changes[i].new_coefficient
+    end
+    for row in unique(rows)
         nnz = glp_get_mat_row(model, row, C_NULL, C_NULL)
         indices, coefficients = zeros(Cint, nnz), zeros(Cdouble, nnz)
         glp_get_mat_row(model, row, offset(indices), offset(coefficients))
-        index = something(findfirst(isequal(col), indices), 0)
-        if index > 0
-            coefficients[index] = changes[i].new_coefficient
-        else
-            push!(indices, cols[i])
-            push!(coefficients, changes[i].new_coefficient)
+        idxs_changed_in_row = findall(x -> x == row, rows)
+        for i in idxs_changed_in_row
+            index = something(findfirst(isequal(cols[i]), indices), 0)
+            if index > 0
+                coefficients[index] = coefs[i]
+            else
+                push!(indices, cols[i])
+                push!(coefficients, coefs[i])
+            end
         end
         glp_set_mat_row(
             model,

test/MOI_wrapper.jl

@@ -586,7 +586,7 @@ function test_multiple_modifications()
     fc1 = MOI.get(model, MOI.ConstraintFunction(), ci1)
     @test MOI.coefficient.(fc1.terms) == [4.0, 1.0, 1.0]
     fc2 = MOI.get(model, MOI.ConstraintFunction(), ci2)
-    @test MOI.coefficient.(fc2.terms) == [2.0, 1.0, 0.5]
+    @test MOI.coefficient.(fc2.terms) == [0.5, 1.0, 2.0]
 end
 
 end  # module