Print out matrix values in the process of Mata function

[Scarlet Ling]

Hello all,

I was trying to print out intermediate matrix results in order to debug my Mata function. But I failed to find an appropriate built-in function. It seems that printf() can only print out scalar values. Is there another function to use? If not, how would you usually debug your codes in Mata?

Thank you in advance!

[Joseph Coveney]

At the point in you code (inside the function you're creating) where you want the matrix to be displayed, write the name of the matrix to the far left side of your text editor. An example is shown below with a matrix named M inside a function.

void function showMatrix(real matrix M) {
    
    printf("\nI'm going to display a matrix for debugging purposes\n")
// Start displaying
M
// End displaying

    printf("I've shown you how\n")
}

It's illustrated below in a use case where I call the Mata function from within Stata.

.ÿ
.ÿversionÿ16.1

.ÿ
.ÿclearÿ*

.ÿ
.ÿlocalÿline_sizeÿ`c(linesize)'

.ÿsetÿlinesizeÿ79

.ÿ
.ÿmata:
-------------------------------------------------ÿmataÿ(typeÿendÿtoÿexit)ÿ-----
:ÿmataÿsetÿmatastrictÿon

:ÿ
:ÿvoidÿfunctionÿshowMatrix(realÿmatrixÿM)ÿ{
>ÿÿÿÿÿ
>ÿÿÿÿÿÿÿÿÿprintf("\nI'mÿgoingÿtoÿdisplayÿaÿmatrixÿforÿdebuggingÿpurposes\n")
>ÿ//ÿStartÿdisplaying
>ÿM
>ÿ//ÿEndÿdisplaying
>ÿ
>ÿÿÿÿÿÿÿÿÿprintf("I'veÿshownÿyouÿhow\n")
>ÿ}

:ÿ
:ÿend
-------------------------------------------------------------------------------

.ÿ
.ÿsetÿlinesizeÿ`line_size'

.ÿ
.ÿ*
.ÿ*ÿDemonstration
.ÿ*
.ÿ
.ÿtempnameÿMyMatrixÿ

.ÿmatrixÿinputÿ`MyMatrix'ÿ=ÿ(1ÿ2ÿ3ÿ\ÿ4ÿ5ÿ6ÿ\ÿ7ÿ8ÿ9)

.ÿ
.ÿmata:showMatrix(st_matrix("`MyMatrix'"))

I'mÿgoingÿtoÿdisplayÿaÿmatrixÿforÿdebuggingÿpurposes
ÿÿÿÿÿÿÿ1ÿÿÿ2ÿÿÿ3
ÿÿÿÿ+-------------+
ÿÿ1ÿ|ÿÿ1ÿÿÿ2ÿÿÿ3ÿÿ|
ÿÿ2ÿ|ÿÿ4ÿÿÿ5ÿÿÿ6ÿÿ|
ÿÿ3ÿ|ÿÿ7ÿÿÿ8ÿÿÿ9ÿÿ|
ÿÿÿÿ+-------------+
I'veÿshownÿyouÿhow

.ÿ
.ÿ
.ÿexit

endÿofÿdo-file


.