I have a zsh script that should generate a bunch of Z-matrix files, but it exits the while loops after one iteration. N and M never increase 

```
#!/bin/zsh
n=0.5 
m=0.5
a=60.0
i=1

while [[ $n -le 1.5 ]];do
    while [[ $m -le 1.5 ]];do
        while [[ $a -le 160 ]];do
            echo $i
            echo "o" > H2O.$i.Z
            eval echo "h  1" $n >> H2O.$i.Z
            eval echo "h  1" $m "2" $a >> H2O.$i.Z

            let i=$i+1
            let a=$a+5.0
        done
        let m=$m+0.05
    done
    let n=$n+0.05
done

```

I'm new to zsh; is my syntax wrong?