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# bvpxtend

Form guess structure for extending boundary value solutions

## Syntax

solinit = bvpxtend(sol,xnew,ynew)
solinit = bvpxtend(sol,xnew,extrap)
solinit = bvpxtend(sol,xnew)
solinit = bvpxtend(sol,xnew,ynew,pnew)
solinit = bvpxtend(sol,xnew,extrap,pnew)

## Description

solinit = bvpxtend(sol,xnew,ynew) uses solution sol computed on [a,b] to form a solution guess for the interval extended to xnew. The extension point xnew must be outside the interval [a,b], but on either side. The vector ynew provides an initial guess for the solution at xnew.

solinit = bvpxtend(sol,xnew,extrap) forms the guess at xnew by extrapolating the solution sol. extrap is a string that determines the extrapolation method. extrap has three possible values:

• 'constant'ynew is a value nearer to end point of solution in sol.

• 'linear'ynew is a value at xnew of linear interpolant to the value and slope at the nearer end point of solution in sol.

• 'solution'ynew is the value of (cubic) solution in sol at xnew.

The value of extrap is case-insensitive and only the leading, unique portion needs to be specified.

solinit = bvpxtend(sol,xnew) uses the extrapolating solution where extrap is 'constant'. If there are unknown parameters, values present in sol are used as the initial guess for parameters in solinit.

solinit = bvpxtend(sol,xnew,ynew,pnew) specifies a different guess pnew. pnew can be used with extrapolation, using the syntax solinit = bvpxtend(sol,xnew,extrap,pnew). To modify parameters without changing the interval, use [] as place holder for xnew and ynew.

## See Also

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