# ODE: no method matching similar
**URL:** https://discourse.julialang.org/t/ode-no-method-matching-similar/40764
**Category:** General Usage
**Tags:** diffeq
**Created:** [June 4, 2020, 8:55pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764 "2020-06-04T20:55:26Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@99dB](https://discourse.julialang.org/u/99dB)
#### Post date: [June 4, 2020, 8:55pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/1 "2020-06-04T20:55:27Z")
Hi All,
I try to compile an ODE model of 1 variable u but I need an if statement based on t.
like something:
```julia
function dudt!(du,u,p,t)
if rem(t,10) < 5
pp = p[1]*t;
end
du = pp*u
end
```
But I get the following message:
```julia
MethodError: no method matching similar(::Float64)
```
Do you have any ideas?
Many thanks!
---
### Author:  [@jonniedie](https://discourse.julialang.org/u/jonniedie)
#### Post date: [June 4, 2020, 9:05pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/2 "2020-06-04T21:05:47Z")
Not sure if this will fix it because I don’t have the whole picture, but change `du = pp*u` to `du .= pp*u` for updating `du` in-place.
---
### Author:  [@99dB](https://discourse.julialang.org/u/99dB)
#### Post date: [June 4, 2020, 9:14pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/3 "2020-06-04T21:14:10Z")
Thanks for the insight. That doesn’t work.
I solved the problem by adding a second variable that does not evolve during the time … but that is creepy:
```julia
du[1] = pp*u[1]
du[2] = 0
```
if you have better ideas! 🙂
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [June 4, 2020, 9:15pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/4 "2020-06-04T21:15:09Z")
Was your initial condition a scalar? If it’s a scalar, why are you using the in-place form?
---
### Author:  [@99dB](https://discourse.julialang.org/u/99dB)
#### Post date: [June 4, 2020, 9:42pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/5 "2020-06-04T21:42:25Z")
Yes it is a scalar. I am new to Julia so I don’t really understand what is the in-place form?
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [June 4, 2020, 9:46pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/6 "2020-06-04T21:46:38Z")
`(du,u,p,t)` is in-place, modifying `du`. If you want to use scalars, use out-of-place:
```julia
function dudt(u,p,t)
if rem(t,10) < 5
pp = p[1]*t;
end
return pp*u
end
```
(the function doesn’t make sense of course because `pp` isn’t always defined). This is explained in the tutorial: [Ordinary Differential Equations · DifferentialEquations.jl](https://diffeq.sciml.ai/latest/tutorials/ode_example/)
---
### Author:  [@99dB](https://discourse.julialang.org/u/99dB)
#### Post date: [June 4, 2020, 9:57pm UTC](https://discourse.julialang.org/t/ode-no-method-matching-similar/40764/7 "2020-06-04T21:57:29Z")
Many thanks @ChrisRackauckas! It is working super well now. I understand the in-place now.