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#!/usr/bin/awk -f

### lin_reg1.awk
# simple linear regression between columns

BEGIN {
    sign = "[+-]?"
    decimal = "[0-9]+[.]?[0-9]*"
    fraction = "[.][0-9]*"
    exponent = "([Ee]" sign "[0-9]+)?"
    number = "^" sign "(" decimal "|" fraction ")" exponent "$"
}

NR == 1 {
    for (n=1; n<=NF; n++)
        ($n ~ number) ? header[n] = "col" n : header[n] = $n
}

NF > 0 {
    if (NF > nf_max)
        nf_max = NF

    ### iterate over columns
    for (y=1; y<=nf_max; y++) {
        if ($y == header[n])
            continue
        if ($y ~ number) {

            ### mean
            count[y] += 1
            sum[y] += $y
            sum2[y] += $y*$y
            delta0[y] = $y - mean[y]
            mean[y] += delta0[y]/count[y]
            delta1[y] = $y - mean[y]
            sum_delta[y] += delta1[y]
            sum_delta2[y] += delta0[y]*delta1[y]


            # x = row, y = col, trendline: y = A + Bx
            for (x=1; x<=nf_max; x++) {
                count[x,y] += 1
                sum_xy[x,y] += $x*$y
                sum_delta_xy[x,y] += delta0[x]*delta1[y]

                # correlation
                r_den[x,y] = sqrt(sum_delta2[x]*sum_delta2[y])
                (r_den[x,y]) ? r[x,y] = sum_delta_xy[x,y]/r_den[x,y] : r[x,y] = 1

                ab_den[x,y] = (count[x,y]*sum2[x] - sum[x]*sum[x])
                if (ab_den[x,y]) {
                    a[x,y] = (sum[y]*sum2[x] - sum[x]*sum_xy[x,y])/ab_den[x,y]
                    b[x,y] = (count[x,y]*sum_xy[x,y] - sum[x]*sum[y])/ab_den[x,y]
                }
                else {
                    a[x,y] = 0
                    b[x,y] = 1
                }
            }
        }
        else
            continue
    }
}

END {
    for (y=1; y<=nf_max; y++) {
        for (x=1; x<=nf_max; x++) {
            if (x != y && r[x,y]) {
                printf(OFMT OFS "(%s)" OFS " = " OFMT "(%s)" OFS " + " OFMT ORS,
                    10.0*log(r[x,y]*r[x,y])/log(10.0),
                    header[y], b[x,y],
                    header[x], a[x,y])
            }
        }
    }
}