无需 IML (SAS) 即可计算矩阵乘法

Question

我从“Dmitry Shopin”的答案中找到了无需 IML 即可计算矩阵乘法的方法。 https://stackoverflow.com/a/22007409/17754000

%macro prod_mat_merge(in_A =,in_B=,ou_AB=);
/*determine number of rows and columns in the 2nd matrix*/
%let B_id=%sysfunc(open(&in_B));
%let B_rows=%sysfunc(attrn(&B_id,nobs));
%let B_cols=%sysfunc(attrn(&B_id,nvars));
%let rc=%sysfunc(close(&B_id));

/*transpose the 2nd matrix*/
proc transpose data=&in_B out=t&in_B(drop=_:);run;

/*making Cartesian product of the 1st and transposed 2nd matrices*/
data &ou_AB;
    do until(eofA);
        set &in_A end=eofA;
        do i=1 to n;
            set t&in_B nobs=n point=i;
            output;
        end;
    end;
run;

/*multiplication*/
data &ou_AB;
    /*new columns for products, equal to number of columns in the 2nd matrix*/
    array p[&B_cols];
    do j=1 to &B_cols;
        p[j]=0;
        set &ou_AB;
        array col _ALL_;
        /*multiply corresponding pairs of columns*/
        do i=&B_cols+2 to &B_cols+1+&B_rows;
            p[j]+col[i]*col[i+&B_rows];
        end;
    end;
    output;
    keep p:;
run;
%mend prod_mat_merge;

但是，我希望 P[j] 都是相同，因为 i 的循环独立于 j。

    do i=&B_cols+2 to &B_cols+1+&B_rows;
        p[j]+col[i]*col[i+&B_rows];
    end;

我还认为数组 P 应该具有 (A_rows*&B_cols) 行和 (&B_cols) 列。

但结果 P 是一个 (A_rows × &B_cols) 矩阵。

这是怎么发生的？