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Goal for Week 4: Reading and writing numbers to files

Summary of new tools and commands.

`load` import columns of numbers from an text file or variables from a MATLAB file.
`save` Save variable values to a MATLAB file.
`sum` add numbers in a vector or table.
`find` return the indexes of values in an array for which a logical test is true.
`isnan` returns true if the variable in a list is "Not-a-Number" or "NaN"; otherwise false.
`length` returns the number of elements in a vector.
`size` returns the number of values in each dimension of a variable.
`csvread` reads a file containing numbers separated by commas (an Excel csv file).
`dlmread` reads a file containing numbers separated by some delimiter character.
`csvwrite` write a matrix to a file with comma delimiters.
`dlmwrite` write a matrix with the indicated delimiter.

Tasks for Week 4
	Tasks
1	Read values from a file containing columns of numbers. Calculate mean values and create a new variable containing differences from the mean.
2	Save variables to MATLAB (.mat) files. Recover variables from MATLAB files.
3	Reading data from excel files (.csv or .xls)
4	Missing values (NaN = Not a Number). Avoiding missing values. using find and sum. subsets of data with indexing. Other special variable values (e, inf, i, j).
5	Writing values to a text file.

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email: J. Klinck