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# biplot

## Sintaxis

```biplot(coefs) h = biplot(coefs,'Name',Value) ```

## Description

`biplot(coefs)` creates a biplot of the coefficients in the matrix `coefs`. The biplot is 2-D if `coefs` has two columns or 3-D if it has three columns. `coefs` usually contains principal component coefficients created with `pca`, `pcacov`, or factor loadings estimated with `factoran`. The axes in the biplot represent the principal components or latent factors (columns of `coefs`), and the observed variables (rows of `coefs`) are represented as vectors.

A biplot allows you to visualize the magnitude and sign of each variable's contribution to the first two or three principal components, and how each observation is represented in terms of those components.

`biplot` imposes a sign convention, forcing the element with largest magnitude in each column of `coefs` to be positive. This flips some of the vectors in `coefs` to the opposite direction, but often makes the plot easier to read. Interpretation of the plot is unaffected, because changing the sign of a coefficient vector does not change its meaning.

`biplot` scales the scores so that they fit on the plot: It divides each score by the maximum absolute value of all scores, and multiplies by the maximum coefficient length of `coefs`. Then `biplot` changes the sign of score coordinates according to the sign convention for the `coefs`.

`h = biplot(coefs,'Name',Value)` specifies one or more name/value input pairs and returns a column vector of handles to the graphics objects created by `biplot`. The `h` contains, in order, handles corresponding to variables (line handles, followed by marker handles, followed by text handles), to observations (if present, marker handles followed by text handles), and to the axis lines.

### Argumentos de par nombre-valor

 `'Scores'` Plots both `coefs` and the `scores` in the matrix `scores` in the biplot. `scores` usually contains principal component scores created with `pca` or factor scores estimated with `factoran`. Each observation (row of scores) is represented as a point in the biplot. `'VarLabels'` Labels each vector (variable) with the text in the character array, string array or cell array `varlabels`. `'ObsLabels'` Uses the text in the character array, string array or cell array `obslabels` as observation names when displaying data cursors. `'Positive'` `true` — restricts the biplot to the positive quadrant (in 2-D) or octant (in 3-D).`false` — makes the biplot over the range ```+/- max(coefs(:))``` for all coordinates. Predeterminado: `false` `'PropertyName'` Specifies optional property name/value pairs for all Line Properties graphics objects created by `biplot`.

## Ejemplos

contraer todo

`load carsmall`

Define the variable matrix and delete the rows with missing values.

```x = [Acceleration Displacement Horsepower MPG Weight]; x = x(all(~isnan(x),2),:);```

Perform a principal component analysis of the data.

`[coefs,score] = pca(zscore(x));`

View the data and the original variables in the space of the first three principal components.

```vbls = {'Accel','Disp','HP','MPG','Wgt'}; biplot(coefs(:,1:3),'Scores',score(:,1:3),'Varlabels',vbls);``` 