[sql-server] How do I call a SQL Server stored procedure from PowerShell?

I include invoke-sqlcmd2.ps1 and write-datatable.ps1 from http://blogs.technet.com/b/heyscriptingguy/archive/2010/11/01/use-powershell-to-collect-server-data-and-write-to-sql.aspx. Calls to run SQL commands take the form:
Invoke-sqlcmd2 -ServerInstance "<sql-server>" -Database <DB> -Query "truncate table <table>"
An example of writing the contents of DataTable variables to a SQL table looks like:
$logs = (get-item SQLSERVER:\sql\<server_path>).ReadErrorLog() Write-DataTable -ServerInstance "<sql-server>" -Database "<DB>" -TableName "<table>" -Data $logs
I find these useful when doing SQL Server database-related PowerShell scripts as the resulting scripts are clean and readable.