```
# one root
IRR(cf <- c(-900, -250+450-90, 460-100, 500-120, 550-140))
# several IRR solutions
IRR(cf = c(-100, 500, -600))
# no solution
IRR(cf = c(-100, 400, -600))
# negative and huge solution
IRR(cf = c(-100, 1000, -600), interval = c(-1.5, 1000))
```

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