R Exercises | Programming Exercises for Finance in the R Language

Math and Stats: Exercises

5. Matrix-vector multiplication. The matrix, X, and vector, Y, have been defined for you. You can check the dimensions of a matrix or vector in R with the dim() function.

In order to perform matrix-vector multiplication, the number of columns of the first matrix (or vector) must be equal to the number of rows of the second. Multiply the X and Y in the order that makes it a conformable operation using the %*% operation.



                                X <- matrix(c(1,0,0,0,1,0,0,0,1), nrow=3, ncol=3)
                                Y <- matrix(c(1,2,3), nrow=1, ncol=3)



                            # Compute the dimensions of X.
                            ___(X)

                            # Compute the dimensions of Y.
                            ___

                            # Multiply X and Y in the correct order.
                            ___ ___ ___



                            # Compute the dimensions of X.
                            dim(X)

                            # Compute the dimensions of Y.
                            dim(Y)

                            # Multiply X and Y in the correct order.
                            Y %*% X


                            test_error()
                            test_function("dim", incorrect_msg="Did you use the `dim()` function?")
                            success_msg("Excellent work. What happens if you switch the order of Y and X?")

You can use the dim() function to check a matrix's dimensions.

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