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# mvnrmle

Multivariate normal regression (ignore missing data)

## Syntax

```[Parameters,Covariance,Resid,Info] = mvnrmle(Data,Design,MaxIterations,TolParam,TolObj,Covar0,CovarFormat)
```

## Arguments

 `Data` `NUMSAMPLES`-by-`NUMSERIES` matrix with `NUMSAMPLES` samples of a `NUMSERIES`-dimensional random vector. If a data sample has missing values, represented as `NaN`s, the sample is ignored. (Use `mvnrmle` to handle missing data.) `Design` Matrix or a cell array that handles two model structures: If `NUMSERIES = 1`, `Design` is a `NUMSAMPLES`-by-`NUMPARAMS` matrix with known values. This structure is the standard form for regression on a single series.If `NUMSERIES` ≥ `1`, `Design` is a cell array. The cell array contains either one or `NUMSAMPLES` cells. Each cell contains a `NUMSERIES`-by-`NUMPARAMS` matrix of known values.If `Design` has a single cell, it is assumed to have the same `Design` matrix for each sample. If `Design` has more than one cell, each cell contains a `Design` matrix for each sample. `MaxIterations` (Optional) Maximum number of iterations for the estimation algorithm. Default value is `100`. `TolParam` (Optional) Convergence tolerance for estimation algorithm based on changes in model parameter estimates. Default value is `sqrt(eps)` which is about 1.0e-8 for double precision. The convergence test for changes in model parameters is `$‖Para{m}_{k}-Para{m}_{k-1}‖` where `Param` represents the output `Parameters`, and iteration k = 2, 3, ... . Convergence is assumed when both the `TolParam` and `TolObj` conditions are satisfied. If both `TolParam` ≤ `0` and `TolObj` ≤ `0`, do the maximum number of iterations (`MaxIterations`), whatever the results of the convergence tests. `TolObj` (Optional) Convergence tolerance for estimation algorithm based on changes in the objective function. Default value is eps ∧ 3/4 which is about 1.0e-12 for double precision. The convergence test for changes in the objective function is `$|Ob{j}_{k}-Ob{j}_{k-1}|<\text{\hspace{0.17em}}TolObj×\left(1+|Ob{j}_{k}|\right)$`for iteration k = 2, 3, ... . Convergence is assumed when both the `TolParam` and `TolObj` conditions are satisfied. If both `TolParam` ≤ `0` and `TolObj` ≤ `0`, do the maximum number of iterations (`MaxIterations`), whatever the results of the convergence tests. `Covar0` (Optional) `NUMSERIES`-by-`NUMSERIES` matrix that contains a user-supplied initial or known estimate for the covariance matrix of the regression residuals. `CovarFormat` (Optional) Character vector that specifies the format for the covariance matrix. The choices are: `'full'` — Default method. Compute the full covariance matrix.`'diagonal'` — Force the covariance matrix to be a diagonal matrix.

## Description

`[Parameters,Covariance,Resid,Info] = mvnrmle(Data,Design,MaxIterations,TolParam,TolObj,Covar0,CovarFormat)` estimates a multivariate normal regression model without missing data. The model has the form

`$Dat{a}_{k}\sim N\left(Desig{n}_{k}×Parameters,\text{\hspace{0.17em}}Covariance\right)$`

for samples k = 1, ... , `NUMSAMPLES`.

`mvnrmle` estimates a `NUMPARAMS`-by-`1` column vector of model parameters called `Parameters`, and a `NUMSERIES`-by-`NUMSERIES` matrix of covariance parameters called `Covariance`.

`mvnrmle(Data, Design)` with no output arguments plots the log-likelihood function for each iteration of the algorithm.

To summarize the outputs of `mvnrmle`:

• `Parameters` is a `NUMPARAMS`-by-`1` column vector of estimates for the parameters of the regression model.

• `Covariance` is a `NUMSERIES`-by-`NUMSERIES` matrix of estimates for the covariance of the regression model's residuals.

• `Resid` is a `NUMSAMPLES`-by-`NUMSERIES` matrix of residuals from the regression. For any row with missing values in `Data`, the corresponding row of residuals is represented as all `NaN` missing values, since this routine ignores rows with `NaN` values.

Another output, `Info`, is a structure that contains additional information from the regression. The structure has these fields:

• `Info.Obj` – A variable-extent column vector, with no more than `MaxIterations` elements, that contain each value of the objective function at each iteration of the estimation algorithm. The last value in this vector, `Obj``(end)`, is the terminal estimate of the objective function. If you do maximum likelihood estimation, the objective function is the log-likelihood function.

• `Info.PrevParameters``NUMPARAMS`-by-`1` column vector of estimates for the model parameters from the iteration just before the terminal iteration.

• `Info.PrevCovariance``NUMSERIES`-by-`NUMSERIES` matrix of estimates for the covariance parameters from the iteration just before the terminal iteration.

## Notes

`mvnrmle` does not accept an initial parameter vector, because the parameters are estimated directly from the first iteration onward.

You can configure `Design` as a matrix if ```NUMSERIES = 1``` or as a cell array if `NUMSERIES `` 1`.

• If `Design` is a cell array and `NUMSERIES` = `1`, each cell contains a `NUMPARAMS` row vector.

• If `Design` is a cell array and `NUMSERIES` > `1`, each cell contains a `NUMSERIES`-by-`NUMPARAMS` matrix.

These points concern how `Design` handles missing data:

• Although `Design` should not have `NaN` values, ignored samples due to `NaN` values in `Data` are also ignored in the corresponding `Design` array.

• If `Design` is a `1`-by-`1` cell array, which has a single `Design` matrix for each sample, no `NaN` values are permitted in the array. A model with this structure must have `NUMSERIES``NUMPARAMS` with ```rank(Design{1}) = NUMPARAMS```.

• Two functions for handling missing data, `ecmmvnrmle` and `ecmlsrmle`, are stricter about the presence of `NaN` values in `Design`.

Use the estimates in the optional output structure `Info` for diagnostic purposes.

## References

Roderick J. A. Little and Donald B. Rubin. Statistical Analysis with Missing Data., 2nd Edition. John Wiley & Sons, Inc., 2002.

Xiao-Li Meng and Donald B. Rubin. “Maximum Likelihood Estimation via the ECM Algorithm.” Biometrika. Vol. 80, No. 2, 1993, pp. 267–278.

Introduced in R2006a

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