# Method Error when using solve in DifferentialEquations.jl
**URL:** https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435
**Category:** General Usage
**Tags:** question, diffeq
**Created:** [August 23, 2020, 10:39pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435 "2020-08-23T22:39:02Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@anon22248738](https://discourse.julialang.org/u/anon22248738)
#### Post date: [August 23, 2020, 10:39pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/1 "2020-08-23T22:39:02Z")
I’m working through the first example in the Ordinary Differential Equations section of DifferentialEquations.jl documentation, and when I call solve(prob,Tsit5(),reltol=1e-8,abstol=1e-8), I get
MethodError: no method matching f(::Float64, ::DiffEqBase.NullParameters, ::Float64)
I’ve tried uninstalling and reinstalling.
My package status reads:
C:\Users\jmurp.julia\environments\v1.5\Project.toml`
[c52e3926] Atom v0.12.19
[2b5f629d] DiffEqBase v6.45.0
[0c46a032] DifferentialEquations v6.15.0
[e5e0dc1b] Juno v0.8.3
[1dea7af3] OrdinaryDiffEq v5.42.3
[91a5bcdd] Plots v1.6.0
Any help would be appreciated.
---
### Author:  [@jonniedie](https://discourse.julialang.org/u/jonniedie)
#### Post date: [August 23, 2020, 11:26pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/2 "2020-08-23T23:26:23Z")
What does your definition of `f` look like?
(Side note: If you put your code in a block surrounded by triple back-ticks it will be easier to read.)
---
### Author:  [@anon22248738](https://discourse.julialang.org/u/anon22248738)
#### Post date: [August 23, 2020, 11:31pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/3 "2020-08-23T23:31:26Z")
Here is my code.
```julia
using DifferentialEquations
using Plots
f(t,u) = 1.01*u
u0 = .5
tspan = (0.0, 1.0)
prob = ODEProblem(f, u0, tspan)
sol = solve(prob,Tsit5(),reltol=1e-8,abstol=1e-8)
```
---
### Author:  [@jonniedie](https://discourse.julialang.org/u/jonniedie)
#### Post date: [August 23, 2020, 11:42pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/4 "2020-08-23T23:42:50Z")
The function should be:
```julia
f(u,p,t) = 1.01*u
```
---
### Author:  [@jonniedie](https://discourse.julialang.org/u/jonniedie)
#### Post date: [August 23, 2020, 11:50pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/5 "2020-08-23T23:50:21Z")
I think at one point, the function signature looked like `f(t,u)`, similar to the MATLAB convention, but it has since changed to `f(u,p,t)` (or `f(du,u,p,t)` for the in-place version). If you’re looking at documentation that still has `f(t,u)`, it’s out of date.
---
### Author:  [@anon22248738](https://discourse.julialang.org/u/anon22248738)
#### Post date: [August 23, 2020, 11:58pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/6 "2020-08-23T23:58:05Z")
That fixed it, thank you.
It looks like it was old documentation, must have clicked on some old link somewhere.
Thanks again
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [August 23, 2020, 11:59pm UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/7 "2020-08-23T23:59:45Z")
> [@jonniedie](#):
>
> I think at one point, the function signature looked like `f(t,u)` , similar to the MATLAB convention, but it has since changed to `f(u,p,t)` (or `f(du,u,p,t)` for the in-place version). If you’re looking at documentation that still has `f(t,u)` , it’s out of date.
Yeah… I think that was 2017. How was the old link found? I think Google is the only thing that still digs up those old docs.
---
### Author:  [@anon22248738](https://discourse.julialang.org/u/anon22248738)
#### Post date: [August 24, 2020, 12:51am UTC](https://discourse.julialang.org/t/method-error-when-using-solve-in-differentialequations-jl/45435/8 "2020-08-24T00:51:04Z")
It was from google, when I searched “Julia Diffeq Uncertainty” it was the first link.