# findindex

Find numeric index equivalents of named index variables

## Description

example

[numindex1,numindex2,...,numindexk] = findindex(var,strindex1,strindex2,...,strindexk) finds the numeric index equivalents of the named index variables in the optimization variable var.

example

numindex = findindex(var,strindex1,strindex2,...,strindexk) finds the linear index equivalents of the named index variables.

## Examples

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Create an optimization variable named colors that is indexed by the primary additive color names and the primary subtractive color names. Include 'black' and 'white' as additive color names and 'black' as a subtractive color name.

colors = optimvar('colors',["black","white","red","green","blue"],["cyan","magenta","yellow","black"]);

Find the index numbers for the additive colors 'red' and 'black' and for the subtractive color 'black'.

3     1

idxsub = 4

Create an optimization variable named colors that is indexed by the primary additive color names and the primary subtractive color names. Include 'black' and 'white' as additive color names and 'black' as a subtractive color name.

colors = optimvar('colors',["black","white","red","green","blue"],["cyan","magenta","yellow","black"]);

Find the linear index equivalents to the combinations ["white","black"], ["red","cyan"], ["green","magenta"], and ["blue","yellow"].

idx = findindex(colors,["white","red","green","blue"],["black","cyan","magenta","yellow"])
idx = 1×4

17     3     9    15

Create and solve an optimization problem using named index variables. The problem is to maximize the profit-weighted flow of fruit to various airports, subject to constraints on the weighted flows.

rng(0) % For reproducibility
p = optimproblem('ObjectiveSense', 'maximize');
flow = optimvar('flow', ...
{'apples', 'oranges', 'bananas', 'berries'}, {'NYC', 'BOS', 'LAX'}, ...
'LowerBound',0,'Type','integer');
p.Objective = sum(sum(rand(4,3).*flow));
p.Constraints.NYC = rand(1,4)*flow(:,'NYC') <= 10;
p.Constraints.BOS = rand(1,4)*flow(:,'BOS') <= 12;
p.Constraints.LAX = rand(1,4)*flow(:,'LAX') <= 35;
sol = solve(p);
Solving problem using intlinprog.
Running HiGHS 1.6.0: Copyright (c) 2023 HiGHS under MIT licence terms
Presolving model
3 rows, 12 cols, 12 nonzeros
3 rows, 12 cols, 12 nonzeros

Solving MIP model with:
3 rows
12 cols (0 binary, 12 integer, 0 implied int., 0 continuous)
12 nonzeros

Nodes      |    B&B Tree     |            Objective Bounds              |  Dynamic Constraints |       Work
Proc. InQueue |  Leaves   Expl. | BestBound       BestSol              Gap |   Cuts   InLp Confl. | LpIters     Time

0       0         0   0.00%   1160.150059     -inf                 inf        0      0      0         0     0.0s
S       0       0         0   0.00%   1160.150059     1027.233133       12.94%        0      0      0         0     0.0s

Solving report
Status            Optimal
Primal bound      1027.23313332
Dual bound        1027.23313332
Gap               0% (tolerance: 0.01%)
Solution status   feasible
1027.23313332 (objective)
0 (bound viol.)
0 (int. viol.)
0 (row viol.)
Timing            0.01 (total)
0.00 (presolve)
0.00 (postsolve)
Nodes             1
LP iterations     3 (total)
0 (strong br.)
0 (separation)
0 (heuristics)

Optimal solution found.

Intlinprog stopped at the root node because the objective value is within a gap tolerance of the optimal value, options.AbsoluteGapTolerance = 1e-06. The intcon variables are integer within tolerance, options.ConstraintTolerance = 1e-06.

Find the optimal flow of oranges and berries to New York and Los Angeles.

[idxFruit,idxAirports] = findindex(flow, {'oranges','berries'}, {'NYC', 'LAX'})
idxFruit = 1×2

2     4

idxAirports = 1×2

1     3

orangeBerries = sol.flow(idxFruit, idxAirports)
orangeBerries = 2×2

0   980
70     0

This display means that no oranges are going to NYC, 70 berries are going to NYC, 980 oranges are going to LAX, and no berries are going to LAX.

List the optimal flow of the following:

Fruit Airports

----- --------

Berries NYC

Apples BOS

Oranges LAX

idx = findindex(flow, {'berries', 'apples', 'oranges'}, {'NYC', 'BOS', 'LAX'})
idx = 1×3

4     5    10

optimalFlow = sol.flow(idx)
optimalFlow = 1×3

70    28   980

This display means that 70 berries are going to NYC, 28 apples are going to BOS, and 980 oranges are going to LAX.

Create named index variables for a problem with various land types, potential crops, and plowing methods.

land = ["irr-good","irr-poor","dry-good","dry-poor"];
crops = ["wheat-lentil","wheat-corn","barley-chickpea","barley-lentil","wheat-onion","barley-onion"];
xcrop = optimvar('xcrop',land,crops,plow,'LowerBound',0);

Set the initial point to a zero array of the correct size.

x0.xcrop = zeros(size(xcrop));

Set the initial value to 3000 for the "wheat-onion" and "wheat-lentil" crops that are planted in any dry condition and are plowed traditionally.

[idxLand, idxCrop, idxPlough] = findindex(xcrop, ["dry-good","dry-poor"], ...
x0.xcrop(idxLand,idxCrop,idxPlough) = 3000;

Set the initial values for the following three points.

Land      Crops           Method      Value
dry-good  wheat-corn      mechanized  2000
irr-good  barley-chickpea mechanized  3500
idx = findindex(xcrop,...
["dry-good","irr-poor","irr-good"],...
["wheat-corn","barley-onion","barley-chickpea"],...
x0.xcrop(idx) = [2000,5000,3500];

## Input Arguments

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Optimization variable, specified as an OptimizationVariable object. Create var using optimvar.

Example: var = optimvar('var',4,6)

Named index, specified as a cell array of character vectors, character vector, string vector, or integer vector. The number of strindex arguments must be the number of dimensions in var.

Example: ["small","medium","large"]

Data Types: double | char | string | cell

## Output Arguments

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Numeric index equivalent, returned as an integer vector. The number of output arguments must be one of the following:

• The number of dimensions in var. Each output vector numindexj is the numeric equivalent of the corresponding input argument strindexj.

• One. In this case, the size of each input strindexj must be the same for all j, and the output satisfies the linear indexing criterion

var(numindex(j)) = var(strindex1(j),...,strindexk(j)) for all j.

## Version History

Introduced in R2018a