**Picking List Elements Using a Logical List**

The program BOOLLIST picks out elements from a source list based on a logical list (a list that consists of 0s and 1s). 0 represents FALSE (do not pick) and 1 represents TRUE (pick).

For more information and examples, see my last blog entry: http://edspi31415.blogspot.com/2015/08/hp-prime-picking-out-elements-using.html

Note, that weird looking L is not the L character, but is represents the small "L" character. This is accessed from [2nd], [stat] (list), OPS sub-menu, select B for "L" (the last option in this sub-menu). On this listing, I will bold the "

**L**".

**TI-84 Plus: BOOLLIST**

**Input "SOURCE LIST=",**

**⌊**A

Input "LOGICAL LIST=",

**⌊**B

sum(

**⌊**B)→S

S→dim(

**⌊**C)

1→I

1→J

dim(

**⌊**A)→A

dim(

**⌊**B)→B

For(K,1,A)

If

**⌊**B(J)=1

Then

**⌊**A(K)→

**⌊**C(I)

1+I→I

End

1+J→J

If J>B

1→J

End

Pause

**⌊**C

**Matrix by Element Multiplication**

In R, the multiplication operator (*) multiplies matrices element-by-element. To get the proper linear-algebra multiplication of matrices, use the %*% operator. The program MATMLEM implements the former method.

Example:

[A] = [[ 1, 2 ] [ 3, 4 ]]

[B] = [[ 4, 3 ] [ 2, 1 ]]

Running MATMELM returns the matrix [[ 4, 6 ][ 6, 4 ]].

Variables [H], [I], and [J] are used for calculations. Also, like BOOLLIST above, the weird looking L is not the L character, but is represents the small "L" character. This is accessed from [2nd], [stat] (list), OPS sub-menu, select B for "L" (the last option in this sub-menu). On this listing, I will bold the "

**L**".

**TI-84 Plus: MATMELM**

Disp "MATRIX MULTIPLY"

Disp "BY ELEMENT"

Input "[H]=",[H]

Input "[I]=",[I]

dim([H])→

**⌊**H

dim([I])→

**⌊**I

If

**⌊**H(1)≠

**⌊**I(1) or

**⌊**H(2)≠

**⌊**I(2)

Then

Disp "INVALID"

Stop

End

[H]→[J]

For(H,1,

**⌊**H(1))

For(I,1,

**⌊**H(2))

[H](H,I)*[I](H,I)→[J](H,I)

End

End

DelVar

**⌊**H

DelVar

**⌊**I

Disp "[J]="

Pause [J]

If the program is hard to read, please let me know in the comments.

I am about half way through the R introduction programming course. Time flies by when you are having fun.

Eddie

This blog is property of Edward Shore. 2015.

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