运行makefile时出错

Question

这是我的makefile的样子：

.PHONY: all clean

all : 1wchaotic.png

1wchaotic.png : plot-script1.gp duffing stroboscopic points1.data
    gnuplot "$<" > "$@"

points1.data : duffing
    ./duffing -a 1 -b 1 -w 1 -u 0.1 -A 35.5 -t 1000 | ./stroboscopic > points1.data

duffing : duffing.c Makefile
    make

clean :
    rm *~ *.png *.data

---

这是我在运行makefile时得到的：

user@ubuntu:~/HW$ make -f makefile2

./duffing -a 1 -b 1 -w 1 -u 0.1 -A 35.5 -t 1000 | ./stroboscopic > points1.data

make: *** [points1.data] Error 255